Dyeing of Sisal and other Plant Fibres: A Handbook for Craft Instructors (NRI) Part 1: Basic information and essential requirements Materials and equipment Technique Fastness testing

Dyeing of Sisal and other Plant Fibres: A Handbook for Craft Instructors (NRI)

Part 1: Basic information and essential requirements

Materials and equipment

Fibres

Sisal is obtained from the thick leaves of a tropical plant known to the botanist as Agave sisalana (Lock, 1969). It is grown mainly in East Africa and Brazil, most of it on large plantations (see Plate 1) using power driven machines for its extraction, although good quality fibre is extracted by smallholders using simple tools (details can be obtained from TDRI). Henequen is obtained from the leaves of the plant Agave fourcroydes which is grown in Mexico (see Plate 2). It is extracted in a similar way to sisal. Fique and cabuya (Furcraea spp.) from Colombia, and Mauritius fibre (Furcraea gigantea var. willemettiana) are all extracted from leaves (Kirby, 1963).

Abaca is extracted from the leaf-sheath of the plant Musa textilis which is grown mainly in the Philippines, but also in Ecuador (Kirby, 1963). The closely-related banana plant also yields a useful fibre (Jarman et al., 1977).

Fibres extracted from plant stems by resting, such as jute (Corchorus capsularis and C. olitorius) from Bangladesh and India (Dempsey, 1975), and kenaf (Hibiscus cannabinus) from Thailand, can also be dyed using the methods described in this handbook.

Coir (Jarman and Jayasundera, 1975) or coconut fibre (from India and Sri Lanka) is extracted from the husks of the coconut palm Cocos nucifera. The natural brown colour of unbleached coir limits the range of possible hues and the fibre is less readily penetrated by dyes than is sisal. Not all the dyes mentioned in this handbook will therefore be suitable for coin

Selection of fibre

The first step towards good quality colour is to choose suitable material for dyeing. Some strands of sisal are pale cream whilst others are light brown. Different hues (see Glossary) will be produced even though the same recipe is used to dye them. If a uniform colour is required the fibre must therefore be all the same colour. It is important also to choose light-coloured fibre if bright colours are required.

Fibres of different fineness and also fibres from plants grown in different localities will dye differently. Batches from different sources should therefore either be dyed separately or mixed thoroughly before dyeing.

Variation in the chemical composition of fibres can also affect the fastness properties: 'woody' or lignified fibres, such as sisal, jute, and coir, give colours that are less light fast than those on pure cellulosic fibres such as cotton and flax.

Dyeing loose fibre, yarn and cloth

Sisal is best dyed in the form of loose fibre. In yarn or woven structures the sisal is tightly packed and the liquor therefore cannot circulate freely round each fibre strand and the colour will not be evenly distributed throughout the material. Dyed yarns often contain a core of undyed fibres which become exposed during wear, producing a faded appearance. However, this problem does not arise if the sisal is dyed before it is spun. Pad-batch dyeing (see Glossary) gives much better penetration of the dye.

The dyeing of the fibre before spinning has the added advantage that fibres of different colours can be blended (see Glossary) to produce interesting colour effects in the finished yarn. Blended fibres will give a yarn of mixed hues whilst blends of white and coloured fibres will appear of overall lighter colour. Light colours produced in this way will be more light fast than when the dye is in a pale shade in all the fibres.

It is possible to dye fibre in the form of woven cloth or matting but the need to obtain good penetration is just as important as in the case of yarn.

Dyestuffs

Only modern synthetic dyestuffs are dealt with in this handbook. They are readily available in most parts of the world and are easy to use. Natural dyes are of variable composition and hence difficult to match, and their use requires considerable skill (Crouch, 1981).

Different fibres present different dyeing problems, and today dye manufacturers offer dyestuffs designed for particular types of fibres. Although each individual dyestuff can only be used successfully on certain fibres, many dyes are similar and have been grouped into a number of classes according to use. The Colour Index (Society of Dyers and Colourists/American Association of Textile Chemists and Colorists, 1982) gives the classification of dyes; it also lists similar dyestuffs which are available from different manufacturers.

Unfortunately, there are no dyestuffs specially developed for sisal but, since it has similarities to other textile fibres, a number of dyestuffs which may be used to colour sisal can be selected from the wide range of dyes intended, for example, for cotton, wool and polyester. For craft work, however, only the following groups of dyes are recommended:

(i) Reactive
(ii) Direct
(iii) Acid (Anionic)
(iv) Basic (Cationic)
(v) Disperse

Reactive dyes (see Glossary) are generally the most useful group for the craft worker. They can be obtained in small packs and are widely available (see Plate 3). They are also easy to use and give good quality, durable colours. Furthermore, unlike other groups of dyes, they can be used with the mad-batch' (see Glossary) method of dyeing which gives good penetration of the dye into the interior of spun yarns and can also be used for dyeing ropes.

Some colours produced from selected direct and acid dyes (see Glossary) have better light fastness than those produced from reactive dyes. However, many acid and direct dyes have poor-to-moderate water fastness on sisal. For most craft goods (except for floor and wall coverings) high light fastness is rarely needed.

Basic and disperse dyes (see Glossary) generally produce colours of poor light or water fastness, or both, on sisal but they are generally useful when a high degree of durability is not needed (such as for beach hats, which are soon discarded). However, a few of the dyes give colours of good quality.

Identifying dyes

Dyes are often bought from local stores or in bazaars-the craft worker will therefore not always find it easy to identify the group to which a dyestuff belongs. However, for workers who must use such sources the following information should prove useful:

Reactive dyes are easily recognised from the instructions provided. In these it will be stated that the dye is suitable for cotton and linen, and is used in cold water. Soda, or a proprietary brand of fixing agent, will also be used in the process. It may also be stated that the dye is suitable for wool but different instructions are given for dyeing this fibre. 'Dylon Cold' dyes are reactive dyes; but care should be taken that these dyes are not confused with Dylon's similarly-packed 'Multi-purpose' dyes.

Direct dyes are also fairly easy to recognise. The instructions will state that the dyes are suitable for cotton and, possibly, wool. They will instruct the user to apply the dye from hot water to which salt only is added. Some direct dyes sold in the domestic market are also claimed to be suitable for leaf and best fibres.

Acid and basic dyes are difficult to distinguish as both may be used on wool. However, since they are both applied from hot water to which a little acid has been added, correct identification is not of great practical importance. Most dyes that are sold in bazaars, etc. for straw dyeing are basic dyes; dyes recommended for wool alone are probably acid dyes.

It is unlikely that disperse dyes will be found on the domestic market, except in mixtures. Individual craft workers therefore need not consider this type of dye, although it might be used at craft centres.

Multi-purpose dyes are mixtures of dyes designed to colour almost any textile fibre. They can be used on sisal but the shades produced will probably be of poorer water fastness than on other textile fibres. Workers who use these dyes should follow the manufacturer's instructions but should extend the boiling period. The dyes are easily recognised from the instructions since the manufacturers will claim that the dyes are suitable not only for natural fibres such as cotton, linen and wool, but also for synthetic fibres such as acetate, nylon and polyester.

Blending dyes

The craft dyer is often asked to match a particular colour. However, even with a large number of dyes to hand, it is usually not possible to obtain a match with a single dye. Therefore, it is necessary to mix together or blend dyes to obtain a matching shade.

In theory, by blending together in different proportions two or three dyes giving bright hues of yellow, magenta (a bluish red) and cyan (a greenish blue), it is possible to obtain almost any colour. However, suitable dyes with these bright colours are rarely available and are usually expensive, but the practical dyer should be able to produce an adequate shade range from cheaper alternatives.

By making use of the colour map inside the back cover of this handbook the dyer will obtain some idea of the hues which can be obtained by blending together whichever dyes are to hand. The bright colours are located at the edge of the map, and shades typically produced in practical dyeing are enclosed by the lines joining the points marked 'yellow', 'red' end 'blue'. It will be seen from the edge of the map that gradually increasing the proportion of one of these colours relative to another gives a progressive change in hue.

Adding the third colour in increasing proportions gives a progressive dulling, shown by crossing the map from the edge to the grey centre, and produces first either olive greens, navy blues, maroons or browns and (depending on the depth of shade) finally greys and blacks.

The map also gives some idea of the shades which can be obtained by blending dyes which are not yellow, red or blue. With two dyes, a line drawn between their two colours passes approximately through the possible range of hues; with three dyes, lines joining the three colours approximately enclose the possible range of hues.

Dyes from different sources may vary in strength-sometimes even those of the same Colour Index Generic Name (Colour Index Number) from the same manufacturer-therefore the amount of dye needed when matching a hue may vary. When using the same dyestuffs all the time, it is possible to estimate almost exactly the required quantities at the first attempt. However, even slight variations in the dyeing technique will affect the amount of dye taken up and it will therefore usually be necessary to make final adjustments to the blend to produce a colour that is of the desired hue. Table 1 gives examples of the hues obtained on sisal using three ICI 'Procion MX'dyes: Procion Yellow MX-8G, Procion Red MX-5B and Procion Blue MX-3G.

Table 1 - Main hues obtained using mixtures of three ICI 'Procion MX' dyes

Dyes selected for blending must: (i) be compatible with each other, and with the material to be dyed; and (ii) produce colours that are of similar fastness. (Basic dyes are not compatible with direct, reactive or acid dyes since they will react in the dyebath to form a complex).

One cannot be certain that a mixture of dye powders, however thoroughly they are mixed, will remain uniformly distributed in the container. It is better, therefore, either to weigh out the dyes and mix them just before use, or to dissolve them separately and mix the solutions before use.

Chemicals

Certain chemicals are needed in the dyebath either to help the fibre adsorb the dye or to help the dyer produce level colours (colours that are evenly distributed over the fibre surface). Alternative chemicals to those recommended by the dyestuff manufacturer can often be used. The following chemicals are commonly used in dyeing.

Dyeing assistants

Salt

Salt is used with reactive and direct dyes to help the fibre adsorb the dyestuff. Common salt (e.g. that used in cooking), sodium chloride, is normally used nowadays as it is usually cheaper and more readily available than the alternative, Glauber's salt (sodium sulphate). With most dyes either can be used but sometimes a dye manufacturer will indicate the preferred chemical.

Glauber's salt can be obtained in two forms crystalline and calcined. The crystalline form, although dry to the touch, contains water of crystallisation in a quantity approximately equal to the weight of actual sodium sulphate, so that if only crystals are available the quantity used must be twice the required amount of the calcined salt.

The quantity of salt used in the dyebath is usually similar for both the common salt and the calcined Glauber's salt; an equal weight of calcined Glauber's salt may therefore be used as a substitute for the common salt. However, some differences in shade may result from using different types of salt.

Safety note: Glauber's salt although not poisonous should not be taken by mouth.

Soda ash

Soda ash (commercial anhydrous sodium carbonate) is used with reactive and direct dyes. Washing soda crystals can be used as an alternative but, as in the case of Glauber's salt crystals, allowance must be made for the water of crystallisation they contain. Approximately 3 times (2.7 exactly) the weight given for soda ash is needed if washing soda crystals are used. For example, 37.8 9 (14 X 2.7 9) of washing soda must be used to substitute for 14 9 of soda ash to give the correct concentration of sodium carbonate in the dye liquor. As washing soda gradually loses its water of crystallisation it cannot be used to give exact weights of sodium carbonate and it is always preferable to use soda ash-especially when matching shades.

Sodium bicarbonate

Sodium bicarbonate, sometimes called bicarbonate of soda or sodium hydrogen carbonate, is a weak alkali used in pad-batch dyeing (see Glossary) with reactive dyes.

Acids

Acid dyes (including 1: 2 metal complex, see Glossary) and basic dyes are best applied from an acid solution. For dyeing sisal it is recommended that only acetic and formic acids are used. These relatively weak acids are not likely to damage the fibre, but if neither can be obtained dilute sulphuric acid can be used instead. This is a strong acid which is dangerous to handle even when in a dilute solution and, if used to excess, will damage the fibre. The craft worker should never handle concentrated sulphuric acid or attempt to dilute it. Only dilute solutions should be used and these can be obtained from the chemical supplier.

Some ordinary acid dyes will dye deep shades from a dyebath containing acetic acid or vinegar, thus avoiding the need for replacing formic acid with a stronger acid such as sulphuric acid. Acetic acid is also used in the copper after-treatment of selected direct dyes.

Acids are sold commercially at various concentrations and, in order to ensure that the correct amount is used, dyeing instructions give the quantity of the particular acid to be used at a specified concentration. However, the initial concentration of the acid used is not important so long as the final quantity in the dyebath is that required. For instance, it makes no difference whether 60 9 of 30% acid or 30 9 of 60% acid is used.

Acetic acid

Safety note: Acetic acid causes burns. Avoid breathing the vapour and contact with the eyes and skin (see Safety precautions and first aid treatment).

Traditionally, the concentration of acetic acid quoted in dyeing instructions is 30% by weight. Nowadays, however, other concentrations, e.g. 60% or glacial (100%) acetic acid are sometimes quoted. Equivalent quantities are calculated as simple proportions. As acetic acid is sometimes labelled with its specific gravity only, a conversion table is given in Appendix 1, Table A.

Glacial acetic acid can sometimes be obtained from suppliers of photographic chemicals. However, since it is an unpleasant chemical, craft workers should dilute this acid in a measured proportion before use.

Glass, china or enamelled vessels should be used when diluting the acid since the concentrated acid softens or dissolves some plastic materials. The concentrated acid should be used in containers with narrow openings and, when open, should be held well away from the face to avoid breathing the acrid fumes. Since many dyeing instructions specify weights of 30% acid, and since it is easier to measure solutions by volume than by weight, it is suggested that, for convenience, a solution containing 30 grams/litre (9/l) of the 100% acid is prepared; 10 ml of this solution can then be used in place of each gram of 3096 acetic acid in the instructions*. This solution can be prepared safely as follows:

1. If the concentrated acid is supplied in a large bottle carefully pour acid from it into a small bottle using a funnel.

2. Measure 970 ml of water into a measuring cylinder and pour into a one litre bottle. Then pour 30 ml of acid from the small bottle into the cylinder and pour into the litre bottle. Mix thoroughly and label.

Vinegar is a very impure form of acetic acid containing about 5 per cent by weight of acetic acid, but it can be used (6 ml for every 1 g of 30% strength acid needed) if the pure acid cannot be obtained.

Formic acid

Safety note: Formic acid causes burns and is irritating to the skin, eyes and respiratory system. Avoid breathing the vapour and avoid contact with the skin and eyes (see Safety precautions and first aid treatment).

Traditionally, the concentration of formic acid quoted in dyeing instructions is 85%: 100 9 of 85% formic acid contains 85 9 of formic acid.

Quantities of other concentrations are calculated by simple proportion. In Appendix 1, Table B specific gravities and percentage concentration by volume of formic acid are converted to percentage concentration by weight.

Formic acid should be obtainable from suppliers of pharmaceuticals, or industrial or laboratory chemicals. Laboratory grades are of about 98% strength but for practical purposes these may be regarded as 100% formic acid.

Concentrated formic acid is an unpleasant chemical to handle. It should therefore be diluted to a solution containing 85 g/l, 10 ml of which will replace each gram of 85% formic acid required.

Sulphuric acid

Safety note: Sulphuric acid in concentrated form reacts violently with water and should never be used by the craft worker. The concentrated acid burns the eyes and skin severely. Even in diluted form it irritates the eyes and may cause burns; it will irritate the skin and may give rise to dermatitis (see Safety precautions and first aid treatment).

The use of sulphuric acid with sisal is not recommended as it will almost certainly have a tendering (weakening) effect on the fibre. Moreover, it is an extremely corrosive liquid and must be handled very carefully. If craft workers have to use this acid it should be used only in diluted form. Sulphuric acid would normally be used only as an alternative to formic acid, which is stronger than acetic acid, but it could be used carefully as a substitute for the weaker acetic acid if vinegar is not available.

It is suggested that a solution containing 100 9/l is obtained of which 10 ml can be used to replace each gram of 85% formic acid specified in the instructions.

As with formic and acetic acids, sulphuric acid is sold in a range of concentrations. These concentrations are measured in different ways, e.g. degrees Baum‚ (°Be), degrees Twaddell (°Tw), or as specific gravity (Sp.gr.). In Appendix 1, Table C the percentage concentration of sulphuric acid solutions measured in these units is given.

Although in wool dyeing equal amounts of either 85% formic acid or 98% sulphuric acid are used, it is recommended that workers who must use sulphuric acid should experiment a little. It is suggested that only a small amount of acid is added at the commencement of dyeing (e.g. about 0.5 9/100 9 of fibre) with further small additions throughout the dyeing. Alternatively, after the small addition at the commencement of dyeing, the remaining quantity could be added in the final stages of dyeing (e.g. 10 - 15 minutes before removing the fibre from the liquor) or a reduced amount added-probably without adverse effect on the depth of colour produced. Either method could help to preserve the strength of the fibre.

The dyed fibre should be rinsed well and, if possible, steeped in a solution of sodium acetate (4 g/l) before drying in order to remove traces of sulphuric acid from the fibre. This is because sulphuric acid, unlike acetic and formic acids, is not volatile and will become concentrated within the fibre on drying, causing damage to the fibre substance. Sodium acetate may be obtainable from some chemists. If not it will be necessary to contact one of the suppliers of chemicals listed in Appendix 3.

Wetting and penetrating agents

Wetting and penetrating agents are chemicals which, when added to the dyebath, help the water to wet and penetrate the fibre. Most wetting and penetrating agents decrease the size of dye particles in solution. These smaller particles diffuse more rapidly into the fibre and deposit more evenly over the fibre surface. However, because the dye is more soluble, the dye liquor retains more dye and less exhausts (see Glossary) onto the fibre. Nevertheless the improvement in the quality of colours usually justifies the small loss of dyestuff.

A few words of caution are needed on the use of wetting and penetrating agents. There are a large number of these sold under different names by dyestuff manufacturers and the results obtained are not always the same. As in the case of dyes, the agents can be anionic (acidic), cationic (basic), or non-ionic, and the ionic nature of an auxiliary can influence the behaviour of the dye. Anionic wetting agents could, for example, compete with acid dyes for a site on the fibre. This would slow down the rate at which the dye deposits on the fibre and this, although helping the dyer to produce a level colour, would cause the transfer of dye to the fibre to be incomplete at the end of dyeing. Similarly, if an anionic agent is used with a basic (cationic) dye the agent would have a direct affinity for the dye. This could cause the dye to remain in the dye liquor or, if the choice of dye and agent is totally unsuitable, cause an insoluble complex (see Glossary) of the dye and agent to precipitate in the dyebath. It is recommended, therefore, that craft workers use the non-ionic wetting and penetrating agents, such as Synperonic BD, with which the authors have experienced no difficulties using any of the dyes mentioned in this handbook.

Craft workers who are unable to obtain special dyeing auxiliaries should experiment with household detergents (e.g. washing-up liquid). Since these products are mainly anionic they should be used with caution with acid or basic dyes. Soap should not be used, as this would produce scum with hard water.

After-treating agents

Three types of after-treatment are described:

(i) copper after-treatment of selected direct dyes:
(ii) cationic after-treatment of direct and reactive dyes;
(iii) back-tanning of basic dyes.

These treatments are similar in that the dye reacts with the chemical used to form a complex which, being in the form of larger particles than the untreated dye, is more difficult to remove from the fibre, thus improving the water fastness of the colour.

Copper after-treatment

Copper sulphate is an effective after-treatment for improving both the light and water fastness of some, but not all, direct dyes. It is normally supplied as blue crystals which contain water of crystallisation. Instructions for dyeing usually quote the weight of this crystalline copper sulphate needed. There is, however, a white anhydrous form of copper sulphate and if only this can be obtained, the weight required would be 0.64 times the weight specified for crystals. For example, only 3.2 g (5 X 0.64) of anhydrous copper sulphate is needed to replace 5 9 of the crystals. Copper sulphate can be obtained from some pharmacies, as it is sometimes used as a fungicide.

Safety note: Copper sulphate is poisonous. Avoid contact with the skin and eyes (see Safety precautions and first aid treatment).

As an alternative to copper sulphate, some dyestuff manufacturers* offer special copper-containing agents for after-treating suitable direct dyes and will supply instructions for their use. Some examples of these are:

Coprantex B (COY)
Resofix CV (S)

Copper after-treatments often change the hue of the dye considerably. Trials should therefore be carried out to determine whether the final colour will be acceptable.

Cationic after-treatment

The cationic agents used for after-treating direct dyes are examples of auxiliaries that form a complex with acid dyes (see section on wetting and penetrating agents). As the direct dyes are also acid dyes, in the chemical sense, these auxiliaries also form a complex with the direct dyes. Examples of cationic after-treating agents are:

Levogen WW (BAY)
Matexil FC-PN (ICI)

Although the cationic agents form a complex with acid dyes they are normally only used with direct dyes. As the acid dye particles are much smaller than the direct dye particles, the improvement in water fastness of acid dyes is rarely significant, and the resultant changes in hue and loss of light fastness are usually unacceptable. The agents find some use with reactive dyes and the use of selected agents is a promising alternative to hot water washing to make reactive colours fast. As cationic after treatments cause changes in hue and loss of light fastness, only shades which bleed to an unacceptable degree are treated.

Back-tanning

Basic dyes form a relatively insoluble salt with tannic acid. This salt forms a complex with a salt of antimony making it even more insoluble. Thus, the water fastness of basic dyes can be improved by treatment with tannic acid, followed by addition of an antimony salt (usually tartar emetic, the common name for potassium antimony tartrate). This treatment, known as back-tanning, was formerly used with basic dyes on cotton, which has no direct affinity for these dyes.

For sisal, the treatment is only worthwhile with basic colours which have fairly good light fastness, because in general there is little point in improving the water fastness of a dyed fibre which has poor light fastness.

Tannic acid occurs naturally in many plants (especially tree barks) and many craft workers may have a local supply. Tartar emetic (Potassium antimony tartrate) can probably be obtained from pharmacies.

Safety note: Antimony compounds such as tartar emetic are poisonous, some also irritate the skin, eyes and respiratory system. Tartar emetic must therefore be handled with care (see Safety precautions and first aid treatment).

Buying dyestuffs and chemicals

Bulk buying

Most large dyestuff manufacturers normally sell dye in minimum packs of 25 kg of a single colour. However, they usually have agencies which will generally supply packs of a size more suited to the small craft dyer. Whilst there is a considerable saving in cost when purchasing dyes in large quantities, only large craft organisations will find it worthwhile.

Buying in small quantities

The UK firm of Durham Chemicals Distributors Ltd (see Appendix 3 for address) will supply, on a cash with order basis, their own dyestuffs and auxiliary chemicals, and a very large selection of those from ICI and BASF, in quantities as small as 1 kg or even 100 9 with some products (e.g. Procion dyes). They will also supply 1 lb packs but these are not standard and would therefore prove more costly.

Dylon dyes are sold in small packs, and should be available to most craft workers from their local store or market. Packs are of three sizes ranging from about 6 9 to 500 9. Dylon International Ltd (see Appendix 3 for address) will no doubt advise on sources of supply in case of difficulty.

Dyes packaged for home dyeing can usually be obtained from local stores or bazaars. Hints on identifying these are given on p.16.

Craft workers will probably have to obtain disperse dyes directly from the dyestuff manufacturers or their agents.

Equipment

Dye vat

A metal dye vat should be used if it is to be heated directly over a flame. However, when heating is by steam, or with an electric immersion heater, the vessels can be made from a wide variety of materials such as wood, concrete (acid resistant), glazed pottery, or high-melting-point plastics. However, with absorbent materials such as untreated wood, use of a vessel must be confined to a specific dye.

Many dyestuffs are spoilt by the presence of iron or copper. Also, the acids and alkalis used in dyeing attack many metals. Therefore, rusty or bare metal containers must not be used. However, with stainless steel, or enamelled iron or enamelled copper containers there is little risk of contamination. Vessels used for washing fibre can be made of metal, such as zinc (galvanised steel), but not metals which rust.

Where there is a number of dyers all dyeing small quantities of fibre it could save time and money if they formed a dyeing co-operative to purchase a large communal dye vat and to buy dyes and chemicals in bulk.

Other equipment

Scales and measures will be needed if the dyer has to control accurately the hue and depth of colour obtained. Accurate measures make possible the matching of shades on separate batches of fibre-an essential requirement for some customers.

Two or three graduated vessels will be required for accurate measuring of large and small volumes; also a large-capacity scale for weighing the material to be dyed to an accuracy of 1 9, and a low-capacity scale (e.g. a simple chemical laboratory type balance accurate to 0.1 9) for weighing the dyestuffs and other chemicals.

Measuring water into the dye vat in large-scale operations is tedious when using graduated vessels, and the use of a dipstick will save time. A dipstick can be made by cutting a notch in a straight pole to mark the depth of water in the dye vat at, say, 5-litre intervals the first time the dye vat is filled. A separate dipstick will be needed for each dye vat of different shape or size.

In addition to the equipment mentioned so far, a stout rod for stirring, a robust thermometer, and lines on which to dry the fibre are useful. For large-scale operations, some form of hoist for lifting wet fibre from the dyebath would be very useful (see Plate 4).

Technique

Basic principles

The main purpose of dyeing is to make the finished goods more attractive. However, uneven dyeing and the presence of loose dye will detract from the appearance. Moreover, the customer will not be pleased if a shower of rain causes the colour to run, spoiling the design and possibly his clothing. Also the goods must be competitive with similar products, and if dyeing adds considerably to the cost of the article or the colours are not sufficiently durable, the prospective purchasers may well turn to alternative products. Cost and durability are both affected by dyeing technique.

It is not possible to describe one ideal dyeing technique, since the choice depends on the customer's requirements and the circumstances of the individual dyer. However, there are certain basic rules that must be followed, and all techniques involve a compromise between quality and economics. The essential steps are given below and form the basis of the dyeing instructions:

1. Select material of uniform colour for dyeing.

2. Choose the colour and decide what fastness properties are required for the end product; then select the cheapest dyestuffs which give these. (For example, it is not necessary to use dyes of high light fastness for party hats that will be used only once-though such an article needs to be moderately water fast to prevent a shower of rain from staining other articles).

3. Choose a dyeing method suitable for use with the chosen dyes. Three methods are mentioned in this handbook:

(i) Exhaust dyeing in which a batch of fibre is dyed from a liquor that is used only once and then discarded. This technique enables dyers to produce matching colours on different batches of fibre with relative ease (provided that the composition of the dye liquor and the dyeing conditions are carefully controlled) but obviously leads to the wastage of chemicals that are not consumed in the dyebath. However, provided that dyes which exhaust well are used, the loss of dyestuff is negligible and other chemicals used in the dyebath are relatively cheap.

(ii) Standing bath dyeing is basically similar to exhaust dyeing. However, after the first dyeing the dyebath is replenished with dyestuff and chemicals and a further dyeing is carried out. This replenishment may be repeated several times. Experience is required to calculate the exact amount of dyestuff and chemicals needed for replenishment.

(iii) Pad-batch dyeing is a recently-developed method based on the use of reactive dyes (see p. 43 and Glossary). It is often (as described by Canning et al., 1977) carried out in the cold and uses low liquor to fibre ratios (1: 1 compared with 20: 1 for exhaust dyeing).

When using either the exhaust or standing bath method:

4. Select dyestuffs that exhaust well onto the material. (If the dyes do not have a strong affinity for the material a large proportion will be lost with discarded dye liquor. Such dyes are best applied by the standing bath technique since this is less wasteful).

5. Make sure that the correct auxiliary chemicals are used in the dyebath.

6. Make certain that all the dye is dissolved before placing any fibre in the dyebath. In order to avoid lumps, first mix acid, direct, reactive and basic dyes to a smooth paste using 2 ml of water or acetic acid solution, as appropriate, for each gram of dye; then add more water to disperse the dye before adding it to the dyebath. With disperse dyes the powders are first sprinkled into water using about 15 ml of water for each gram of dye (the dye will not disperse properly if too much or too little water is used). Lumps of dye in the dyebath will give rise to uneven colours and impaired fastness properties. They should be broken up whilst pasting, and filtering (e.g. through a muslin cloth) should be used only as a last resort.

7. Never place the fibre in a dyebath which is above 50°C. Increase the temperature slowly. Placing the fibre in a hot bath will cause the dyestuffs to be taken up rapidly and the levelling of colour will be difficult to control.

8. Make sure that the dye liquor covers the goods. Thorough and efficient stirring must be used to give good circulation, especially in the warming-up period and the early stages of boiling during which most of the dye exhausts. Inadequate circulation of liquor will result in unevenly coloured fibre. The agitation of the fibre produced by boiling cannot be relied on to distribute the dye evenly.

9. Dyeing must be continued for an hour or more even though the fibre may appear adequately coloured after only a short period of dyeing. The colour built up initially lies at the surface of the fibre and will rub off easily.

10. After removing the fibre from the dyebath it must be rinsed (preferably in running water) to remove adhering dye liquor, otherwise the fibre will become coated with loose dye on drying.

Costs of dyeing

The craft dyer should keep an account of all the various costs involved in dyeing, including his own time and the cost of heating the dyebath. Considering the following questions may help the dyer to find ways to reduce costs:

1. Can the cost of dyestuff be lowered? There is often a cheaper alternative dye. However, sometimes it is advantageous to buy a more expensive dye. The strengths (or tinctorial yields) of dyestuffs differ and it may cost less to use a smaller amount of a stronger dye to produce the same colour.

2. Is too much dye being used? There should only be sufficient dye in the bath to produce the required depth of colour. Too much dye will produce too deep a shade or tempt the dyer to remove the fibre too soon-leading to poor penetration of dye. In either case dye will be wasted.

3. Can less acid be used? Acid is used with both acid and basic dyes. Some acid dyes need less acid to fix them than others and less acid is needed with pale shades than with deep. With basic dyes the acid slows down the adsorption of dye and thus aids levelling. In this case more acid is needed when dyeing pale shades since with these it is less easy to control dye adsorption.

4. Can less salt (or other dyeing assistants) be used? Salt in the dyebath increases the proportion of direct or reactive dye that adsorbs onto the fibre. By using extra salt the dyer can reduce the quantity of dye in the bath. The dyer will need to calculate at what point the cost of salt (or soda or other dyeing assistants) becomes greater than the cost of dyestuff saved

5. Can less fuel be used? Fuel is usually expensive and sometimes hard to find. It may be possible to reduce heating time by increasing the amount of dyeing assistants. It may not be necessary to boil for so long-especially if good penetration is not essential. Insulation of the dyebath will help to reduce fuel consumption.

6. Can less time be used? Not all processes require the craft dyers undivided attention (e.g. the batching operation of pad-batch dyeing); however, most do and the dyer should keep a record of all the time spent exclusively on each separate dyeing. Before extending the time of dyeing to increase the adsorption of dye the dyer should calculate whether it would be cheaper to, for example, add more salt instead.

7. Can less wetting agent be used? Wetting agents assist the production of uniform colours. However, they reduce dyebath exhaustion and thus increase wastage of dye. The minimum amount should therefore be used.

8. Can less water be used? By reducing the quantity of water the dyer can save on dyestuff and assistants since the exhaustion will be increased. Less fuel will be needed to heat a smaller quantity of water. However, the amount of water should not be reduced so much that circulation of liquor is restricted.

Making matching shades

Dyers are often asked to reproduce fashionable colours by blending dyes (see p. 17) or to produce several batches of fibre in identical shades. This latter aspect is important, since marketing organisations need to illustrate goods in catalogues and must be able to supply identical goods on repeat orders.

When producing a new colour for the first time, the experienced dyer starts with a few 'trial and error' test dyeings. These trial dyeings are usually made on a few grams of material. The small quantities of dyestuffs and chemicals required can be measured on an accurate balance but, as an alternative, solutions can be carefully diluted. For example, a dyer who has only kitchen equipment can dissolve one teaspoonful of chemical in four cupfuls of water and, by taking only one cupful of this solution, can scale down the size of operation four times. The small-scale dyer will find this method of working advantageous-especially when working with blends where, for example, 10 teaspoonfuls of dye solution 'A' mixed with 3 teaspoonfuls of dye solution 'B' give exactly the right colour on 250 9 of fibre. Dyers could not measure such small quantities accurately using teaspoons of dye powder. (Unfortunately, this method would be wasteful with reactive dyes as solutions of these become useless if kept for more than a few hours). After the right conditions have been found, the operation can then be scaled up. All that is needed to do this is to increase proportionately the quantities of each ingredient [including the fibre and water) to obtain the required amount of dyed fibre.

By using identical dyebath conditions for each batch of fibre, matching shades can be produced. An experienced dyer always measures the ingredients used in the dyebath and keeps a record of the entire dyeing process. By consulting this record (or 'recipe'}it is possible to reproduce the same colour on a subsequent occasion. However, to obtain identical shades, it may sometimes be necessary to make small adjustments to the dyebath at the conclusion of dyeing.

When dyeing matching shades the quantity of water in the dyebath must be kept constant. Throughout the course of dyeing, water will be lost through evaporation. This water must be replaced, or the concentration of dyestuff will increase and cause increased adsorption of dye. Conversely the addition of too much water when topping up the dyebath will cause a decrease in the quantity of dye adsorbed by the fibre. The water level can be checked with the aid of a 'dipstick' (see p. 25).

In the next section commercial dyeing practices which enable the dyer to reproduce colours accurately are described.

The dyeing recipe

Commercial dyers usually work from a general recipe in which the quantities of ingredients relate to a unit weight of fibre. When using such a recipe only a few simple calculations are needed for dyeing a batch of fibre of any given size. Also, dyestuff manufacturers find the general recipe a convenient method of providing instructions.

The general recipe does not give detailed information on the application of the dyes. However, the quantities of ingredients used are readily derived from information expressed in the following terms 'Liquor ratio', 'percentage' end 'Concentration'. These terms are widely used and, in dyeing, relate the quantity of ingredient to the air-dry weight of the fibre to be dyed.

Liquor ratio (LR)

The liquor ratio (LR) refers to the quantity of water required in the dyebath. The ratio is the weight of liquor required for each unit weight of air-dried fibre to be dyed. For example, a liquor ratio of 20:1 indicates that the weight of liquor required is twenty times the weight of air-dried fibre to be dyed.

It is usual to convert the weight of liquor to a volume, which is more easily measured. In dyeing, the density of the liquor is taken to be equal to that of water (i.e. 1 kg of liquor equals 1 litre). Therefore, with a liquor ratio of 20:1, 20 litres of water will be used for each kilogram of fibre.

Percentage shade

The depth, or intensity, of colour is usually controlled by varying the quantity of dye in the dyebath. In practice, the quantity of dye is expressed as a percentage of the weight of the air-dried fibre to be dyed. Consequently there are a number of terms in common use such as 'per cent shade', 'at .... per cent', 'per cent depth', etc. Whatever term is used in the dyeing recipe, the actual quantity of dye to use in the dyebath is calculated as in the following example in which the weight of dye needed to dye a 0.5 per cent shade on 5 kg of fibre is calculated:

Weight of dye needed	= (Weight of fibre X percentage shade)/100
	= (5,00O g X 0.5)/100
	= 25 g

Actual weights needed in the dyebath of other ingredients given as percentages on the weight of fibre are calculated similarly. However, it is important to make sure that 'percentage on the weight of fibre' is not confused with the 'percentage strength of a chemical solution' used (e.g. acetic acid (30%), acetic acid (60%), formic acid (85%)).

Depth of colour

The term 'percentage shade' is not a direct measure of the depth of colour of the dye. Visual depth of colour depends on the concentration of dye at the surface of the fibre and this will vary at a given percentage depth with differences in dyeing technique (e.g. time of dyeing, liquor ratio, concentration of salt or acid). Different dyestuffs of the same colour, and also the same dyestuffs from different manufacturers, give different visual depths of colour when used at the same percentage shade. Although manufacturers endeavour to maintain consistency, recipes should be checked, and adjusted if necessary, each time a new batch of dye is used.

Concentration

Quantities of ingredients are sometimes given as a concentration (e.g. grams/litre, g/l). If, for example, the dyeing recipe specifies salt at a rate of 10 grams/litre (9/l) one must use 10 grams of salt for each litre of dye liquor needed. In order to determine how much ingredient is needed in the bath the actual volume of liquor needed must first be calculated using the liquor ratio (LR) given in the recipe and the weight of the fibre to be dyed. A typical calculation of the quantities of ingredients needed is given in the following example

3 kg of fibre is to be dyed at a liquor ratio of 20:1. The recipe specifies 5 g/l of salt in the dye liquor

(i) The quantity of water needed is

Water at LR of 20:1 = 20 X weight (kilograms) of fibre = 20 X 3 kg = 60 litres

(ii) The quantity of salt needed is:

Salt at 5g/l = 5 9 X volume (litres) of liquor = 5g X 60 = 300 g.

Concentrations of chemicals used in the dyebath are now commonly expressed as parts/1,000 (parts by weight of dye liquor). However, the more traditional units of 9/l and Ib/100 gallons are equivalent since 1 litre of water weighs 1,000 g and 100 gallons of water weigh 1,000 lb.

Completion of the recipe

The same dyeing time, dyeing temperature and sequence of operations are used irrespective of the size of the batch of fibre.

Fastness testing

Introduction

Many chemicals and environmental factors can cause colours to change their depth of shade and also, occasionally, their hue. Some changes are caused by the physical removal of dye and, whilst the visual colour may not be affected, this removed dye may stain adjacent materials.

Colour fastness is not solely a property of the dye. Fastness properties are also affected by the material on which the dyestuff is used. Sisal, for example, unlike cotton, contains substances which contribute to the action of light in fading the dyes and most dyes are, therefore, less light fast on sisal than they are on cotton. The substances in sisal usually turn brown, causing the colour of the dyed material to change. Colour fastness of a dye is also dependent on depth of shade. Deep shades resist light better than pale shades of the same dye, but dye is more readily lost by physical means from deep shades, leading to reduced water fastness and greater risk of staining onto other materials.

When evaluating dyes it is important that the depth of colour can be described accurately to allow fair comparisons between dyes. This is usually done with the aid of pattern cards which illustrate and describe hues in terms of internationally agreed standard depths of colour. Such pattern cards conform to ISO Recommendations R105 and include British Standard BS1006: Section A01: 1978, Standard depth: matt. Only colours of equal visual depth can be usefully compared.

When choosing dyes, the dyer must consider colour fastness from two aspects: firstly, the changes of colour that could occur during subsequent processing of the dyed material; and secondly, changes that could occur during use of the finished article.

After-treatment of some dyes (e.g. directs) to improve their water fastness, or subsequent application of lacquers to the finished goods, may cause change of colour. The change, of course, is important if the dyer is aiming to produce a specific colour on the finished goods and the dyer must then know what changes will take place so that compensation can be made for them. For craft workers who make hats, fastness to dry heat is of importance: hats are often formed on hot moulds, or by ironing, and these processes could cause loss of dye.

Colour fastness in use is far more important. Many dyed goods are necessarily exposed to adverse treatment during use, for example, by cleaning. With hats and bags, a shower of rain could cause colours to run and stain the user's clothing. Table mats could become wet from spillage and stain the table cloth. Therefore, it is the dyer's responsibility to ensure that the fastness properties of the colours produced are suited to the goods for which the material is to be used.

All colours fade in use, but provided that this is consistent with age it does not worry the user seriously. However, if each colour changes to a different extent, or changes in the hue occur, the art design may be spoilt and this the user will find unacceptable. Therefore, colours of similar fastness must be used on individual articles and blends must be prepared from dyes with similar fastness properties.

Fastness requirements of sisal goods can be expected to be less stringent than those for cotton and woollen goods. It is very unlikely, for example, that sisal will be washed with hot water and detergents, except when it is used in matting, or that it will be dry-cleaned or bleached, so fastness to these treatments need not be considered. However, fastness to light and cold water (e.g. rain) is of great importance - especially for more expensive durable goods.

Since fastness properties are important, craft workers should test the quality of new dyes before they are used for durable goods. Test methods are described in this section. However, provided that dyeing conditions are not altered it is unnecessary to test subsequent dyeings with the same dye.

There are a number of recognised tests for colour fastness, the results of which can be expressed in numerical terms. For workers who are interested in this subject, a complete set of colour fastness tests (BS 1006: 1978 Methods of test for colour fastness of textiles and leather), based on the recommendations made by the International Organization for Standardization, is available. As it is unlikely that craft workers will have the equipment or expertise to follow these special tests, some alternatives are given here. The basis of these alternative tests is the comparison of performance given by the new dye with that given by one that has proved satisfactory in service.

Water fastness

Tests for water fastness are designed to determine whether water will cause fading, running of colour with spoilage of design, and staining of other goods. To obtain this information the craft worker must carry out two separate tests, each one run concurrently with a similar test conducted on dyed sisal (or other material) that has satisfactory water fastness.

Loss of colour and staining onto undyed sisal (see Figure 1)

The test is done as follows:

1. Take a small portion of sisal (about 10 cm long) dyed with the new dye, and plait it with an equal weight of undyed sisal. Secure the plait at each end, for example, with rubber bands.

2. Immerse the plait in thirty times its own weight of cold, preferably distilled, water for 4 hours (1g water = 1 ml).

3. Remove the plait from the water, separate the dyed and undyed fibre and leave to dry

4. Compare the tested dyed sisal with the untested dyed sisal to assess the degree of change in or loss of shade (if any).

5. Compare the undyed sisal used in the test with some undyed sisal that was not tested, to assess the degree of staining.

Repeat steps 1 - 5 with dyed sisal {or any other material) that is known to have satisfactory water fastness. If the degree of change in shade and staining for the sisal dyed with the new dye is the same or even less than that of the satisfactory dyed sisal or other material then it is safe to use fibre dyed with the new dye.

Figure 1: Water fastness testing: loss of colour and staining onto undyed sisal

Loss of colour and staining onto wool and cotton (see Figure 2)

The test is done as follows:

1. Take two pieces of cloth of approximately equal size (a 5 cm or 2 in. square is suggested), one of which is undyed wool, and the other is undyed cotton, and stitch the cloths together along one edge.

2. Take a portion of sisal dyed with the new dye weighing about half of the combined weight of the cloths and spread this evenly between the two cloths.

Figure 2: Water fastness testing: loss of colour and staining onto wool and cotton

3. Wet the test specimen with cold, preferably distilled, water.

4. Place the wet test specimens between two glass plates weighing approximately 50 9 each and of a size similar to that of the cloths (a 58 mm square of 6 mm thick glass plate weights approximately 50 9).

5. Place the 'sandwich' in a dish and cover with cold, preferably distilled, water.

6. Press the top plate evenly and lightly to remove bubbles of air from between the plates, and then allow to stand for 15 minutes.

7. Without disturbing the plates, pour off the water from the dish (a film of water should remain within the plates).

8. Leave for a further 4 hours, then separate the sisal from the cloths and allow to dry.

Repeat steps 1 - 8 with dyed sisal (or any other material) that is known to have satisfactory water fastness.

9. Place the dyed sisal from the test alongside a portion of the dyed sisal of similar size that has not been tested, and compare the contrast (see Glossary) with that shown by similar portions from the test on the satisfactory dyed sisal. If the colour under test shows equal or less contrast than the proven colour, the fastness with respect to loss of colour is equal to or better than the proven colour.

10. Similarly, place the cloths from the test alongside similar-sized portions of the same materials that have not been used in the tests and compare the contrasts shown with those shown between similarly arranged cloths from a test on the proven colour. Equal or less contrast demonstrates equal or better fastness with respect to staining.

Wool and cotton have been chosen because these two materials are commonly used in clothing. However, if it is known that the fibre will be in contact with other materials, such as nylon or polyester, then a similar test using cloths made of these materials should be carried out.
If in either of the water fastness tests the fibre dyed with the new dye produces a worse staining or has a greater loss of or change in shade than the satisfactory dyed sisal (or other material), then an alternative dye should be tested.

Light fastness

It is important that, having spent much time and trouble on an article, the dyes do not fade quickly.

There are a number of standard tests for light fastness which are used by manufacturers and test houses. Basically these involve comparing the fastness of the test material with that of materials dyed in order of increasing fastness. Materials which are to be used for window curtains have to be of the highest light fastness (8 on the International Organization for Standardization (ISO) scale) whilst for cheap 'throw away' goods such as party hats, light fastness is unimportant. These international standards require special equipment which the craft worker may find difficult to obtain. Fortunately adequate results can be obtained with quite simple equipment (see Figure 3).

A satisfactory test may be carried out by taking a bundle of dyed fibre (about 4 cm long) and mounting it on a card next to a similar-sized bundle of coloured fibres which are known to have satisfactory light fastness. About a quarter of each fibre is covered with an opaque card or aluminium foil and the whole assembly placed under glass in a position facing the mid-day sun. The glass should be at least 5 cm away from the fibre and should allow free circulation of air over the fibres. The specimens are examined daily for fading (shown by a sharp contrast (see Glossary) between the covered and exposed portions) and the performance of the new colour is compared with that of the proven colour. During the test a further cover may be placed over some of the exposed portion, so that the performance over the short term can be compared with that over the long term.

Figure 3: Light fastness testing

The colour used for comparison purposes can be on any fibre, it need not be on sisal. As with the water fastness tests, the dyer can judge from the results whether the new dye is likely to have an acceptable light fastness on sisal.

Light fastness varies with the quality of light. Therefore, in different locations or with different light sources, different light fastness ratings could arise.

Fastness to processing

As mentioned previously, lacquering, hot pressing, and after-treatment of dyes could cause colour changes. If it is important for craft workers to know of these changes it is suggested that a small portion of the dyed fibre be subjected to the processing involved, and compared with the original dyed fibre. Any serious change of colour will then be apparent.