Art of staining & dyeing leather
Introduction
This article discusses the art of staining and dyeing leather, specifically focusing on dyeing Morocco and similar leather using aniline dyes. The author notes that achieving an even tone of color on leather with aniline dyes is more difficult compared to dye-wood liquors, as there are several factors that influence the intensity and tone of the color produced. These factors include the temperature and strength of the dye liquor, the number of pieces of leather being dyed, and the length of time the leather is immersed in the dye bath. Despite these difficulties, aniline dyes are preferred because they can produce much more brilliant colors than dye-wood materials. The author recommends a method of using several baths of dye-liquor, each of different strength, to gradually dye the leather until it reaches the desired color. This method is said to minimize problems such as uneven coloration and bronzed appearance. You may also enjoy our new series on Lessons in Leatherwork.
III. Dyeing Morocco and similar leather
The operation of dyeing with aniline dyes is, in one respect, less easy of an accomplishment than with the dye-wood liquors. With the latter dyeing materials even tones can be obtained at very little trouble. With aniline dyes there are several influences at work which hinder the production of an even tone of colour on the leather. For example, the higher the temperature at which the dye liquor is used the greater will be the intensity of colour produced, also the strength of the dye liquor determines in a remarkable degree the actual tone of colour produced on the leather. A weak dye liquor will give a colour that is no indication whatever of the colour that can be produced with the same dye, when the dye liquor is a strong one. Also if more than one piece of leather is to be dyed, the piece first dipped in the dye liquor will be much more intense in coloration than the next and subsequent pieces. Aniline dyes have such a great affinity for any material of an organic nature that they combine therewith with great rapidity, more so according to the strength of the dye liquor. Yet again, the length of time in which the leather is submitted to the action of the aniline dye bath greatly influences the colour produced.
If the immersion be carried on too long, or the dye liquor be too strong, the colour exhibited on the leather will present a bronzed appearance. Yet with all these apparent difficulties, the colours which can be produced by means of aniline dyes are so much more brilliant than what can be obtained with dye-wood materials, that the novice will do well to practise with the former.
One of the best methods to pursue, because it minimises the troubles above referred to, is to have several baths of dye-liquor, each of different strength, and to submit the leather first to the action of the weakest one, and then to the next stronger one, and finally, to the strongest one of all. By this method the leather is but faintly coloured at first, and any unevenness of coloration is corrected as it successively passes through the stronger dye baths, until, finally, it has assumed the exact colour desired. This method is very much to be preferred to prolonging the time of immersion of the leather in the dye liquor, and as a matter of fact, the desired results are obtained with comparatively few failures.
Preliminary operations in Dyeing with Aniline Colours
Have three or four earthenware vessels to hold the hot dye liquor, and a copper one to warm it in. Instead of a dyeing bath, a zinc or copper tray having a rim about two inches high should be used, when the dyeing may be effected by dipping, in which case a deep earthenware pan (such as is used in the kitchen for storing bread in) should be used. Prepare the dye liquor according to the quantities of ingredients named in the formulae, and, when the dye liquor has been made and filtered, divide it into three (or four) equal quantities to one quantity add three times its bulk of clean water, and to the second quantity add its own bulk of pure water, and call the first quantity No. 1 dye liquor, the second quantity No. 2 dye liquor, and the undiluted portion No. 3 dye liquor. Thus No. 1 would be composed of one-third dye liquor and two-thirds water. No. 2 would be composed of half dye liquor and half water, while No. 3 would be dye liquor of full strength, being undiluted.
Now, when carrying out the dyeing process, put the leather into No. 1 dye liquor first and for the prescribed length of time, then into No 2 dye liquor, and finally into No. 3 dye liquor, observing to keep the temperature of the dye liquor to the proper degree, and also to regulate the length of time of the immersion of the leather. Any unevenness of colour in the lirst two dye liquors will be corrected in the final one by a prolonged immersion before removal from this dye liquor.
Wash the dyed leather in clear water and hang it up to dry, when dry finish it with a finishing gloss. If more than one pair of pieces of leather are to be dyed then make a fresh bath of dye liquor for the final bath (undiluted), and after dyeing the first pair of skins repeat with the dye liquor, and put the second pair of skins first into No. 2 dye liquor, then into No. 3, and finally into the fresh dye bath. By this means an economy of dye liquor is effected, but what is of greater importance a better evenness of coloration is produced. To ensure evenness of coloration the addition of phosphate or sulphate of soda to the dye liquor is frequently made (vide infra, while in some cases the skin should be moistened with a weak solution of either sulphuric acid or soap and water, according to the nature of the aniline dyes made use of, viz., whether it requires an acid or alkaline base to work on.
In dyeing leather it is usual to place flesh side to flesh side, whereby the flesh side does not become fully dyed, and a saving of dye liquor is obtained; but, of course, for the amateur worker, who will probably not care to operate on a whole pair of skins at one operation, this is not necessary, as the amount of dye liquor he will require is very limited. While the leather is in the dye liquor it should often be moved about and examined from time to time to judge to the tone of colour obtained at each stage. When sufficiently coloured, wash the dyed skin in plenty of clean water and hang up to dry.
The subsequent finishing operations consist in giving a slight smear of oil (fish, sweet, or sperm) on the dyed side, and then laying on a thin coating of gum dragon mucilage—prepared as given below—or else a solution of egg albumen mixed with glycerine.
Gum Dragon finish is prepared by soaking 1 oz. to 2 oz. of gum tragacanth (i.e., commonly called gum dragon) in one gallon of cold water for several weeks, and then straining the thick jellylike mucilage that is produced, and picking out all white lumps,, and to the strained mucilage adding one to two fluid ounces of castor oil per gallon of mucilage. This finish is laid on the dyed skin by means of a roll of felt, which is dipped in the mucilage and then lightly rubbed over the dyed leather, and, when dry, the coloured leather is ready for use as required.
Egg Albumen preservative finish is prepared by mixing 30 fluid ounces of egg yolk with 1 fluid ounce of glycerine, and then compounding them with water in the proportion of 1 oz. to 2 oz. per pint of water.
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Formulæ for Dyeing Leather with Aniline Dyes
The following list of formulæ will be sufficient for the novice to try a "’prentice hand" in, and should not be found at all difficult. Any of the preservative finishing glosses can be used with the aniline-dyed leather so as to impart a finished appearance and prevent the colour fading.
H. C. S.
Lilac Colour
Ingredients
- Mordanting fluid
- 5 pints of water
- 1 oz. of tannic acid
Dye Liquor
- Five pints of water
- 1½ drachms (troy) of methyl violet
Finishing Gloss
- 1 oz. good glue
- 5 pints of water
- 1 oz. glycerine
Method of Manipulation
- Well saturate the leather with the mordanting fluid, and then, having made the dye liquor hot (~90°F/32°C), work the leather about therein until the tone of colour desired is obtained, and, after drying, brush it over with the finishing gloss and hang up to dry. The finishing gloss is prepared bysoaking the glue in the water for ten hours, and then melting it therein by boiling and adding the glycerine.
Red Colour
Ingredients
- 5 pints of water
- 1 oz. of eosine A
- 3 oz. acetic acid
- 10 oz. sulphate of soda
Method of Manipulation
- Boil all tin ingredients, strain or filter, and then work the leather in the dye liquor at a temperature of about 90°F. (~32°C) until the desired tone is obtained. No mordant is required with this dye, as the sulphate of soda acts as a leveller or mordant in producing an evenness of coloration.
Red Colour
- Make a dye liquor of magenta, and after dyeing the leather therein, dip it into a bath made up of chrysoidine until the tone of colour is obtained. For a scarlet—Make up a dye liquor of the following ingredients: 5 pints of water, 1½ oz. No. 2 magenta B, 1 oz. auramine, 10 oz. Glauber's salt (sulphate of soda). No mordant required. Work the leather in the dye bath at 90° F. until dyed sufficiently.
Crimson Colour
Ingredients
- Mordant fluid
- 48 grains of borax
- 1 gallon of water
Dye Liquor
- ½ gallon of water
- 3 oz. azo bordeaux (fast crimson)
Method of Manipulation
- Moisten the leather with the borax solution and then make up a bath of dye liquor by adding one fluid ounce of the above solution of the fast crimson to every 80 oz. of water taken, raise the liquid to 110°F. (~43°C), and work the leather therein for ten to fifteen minutes. Then strengthen the dye liquor with a fresh addition of an equal bulk of fresh dye liquor, and dye to tone desired.
Canary Yellow Colour
Ingredients
- 5 pints water
- 1 oz. thioflavial T
- 10 oz. sulphate of soda
- No mordant required; work at 100°F
Full Yellow Colour
Ingredients
- 5 pints water
- 1 oz. auramine
- 10 oz. sulphate of soda
Full Yellow Colour
Ingredients
- 4 pints water
- 1½ oz. orange B R.
- Before using the dye liquor, mordant the leather with a solution of tannin and 1½ drachm (troy) per gallon of water
Light Green Colour
Ingredients
- 5 pints water
- 1 oz. malachite green
- ¼ oz. Nile blue A
- 10 o.z. sulphate of soda
- Work at 100°F.
Dark Green Colour
Ingredients
- 5 pints water
- 1 oz. brilliant green
- ½ oz. chrysoidine
- 10 o.z. sulphate of soda
Light Blue Colour
Ingredients for mordant use
- 72 grains borax per gallon of water
Dye Liquors
- Dissolve 3 oz. soluble blue R in 80 fluid oz. of water
Brown Colour
- Prepare a mordant of tannic acid dissolved in water, 150 grains of acid per 4 pints of water, and for the dye liquor dissolve 150 grains of Bismarck brown per ½ gallon of boiling water, and after filtering dissolve 95 grains of gelatine in the solution and dye the leather in this liquid at a temperature of 100°F.
- As a topping agent for toning down the brightness to a darker brown, lay on with a sponge a solution of 30 to 90 grains of sulphate of iron per 75 fluid oz. of water. After dying the coloured leather, use as a finish the egg yolk preservative already referred to.
Nut Brown Colour
- Prepare a dye liquor of 5 pints of water, 3 oz. benzo brown, 10 oz. common salt. No mordant required; dye at 90° F.