The dyeing of furs with mineral colors involves the precipitation on the fibre in a more or less permanent form of the sulphide, oxide or other insoluble compound of a metal, and can be brought about in several ways. By what is known as double decomposition, that is, by the use of two solutions successively applied, the ingredient of one causing a precipitate to form when in contact with the constituent of the second, the color is produced on the hair. Another method is to use solutions of chemicals which decompose on contact with the hair, forming an insoluble compound. In the first method the hair is alternately treated with the two solutions of the requisite chemicals, drying between each brushing, the process being repeated until the desired shade is obtained. The second method merely requires the solution of the chemical to be applied to the hair, which is then dried, the color forming by itself.
One of the most important of the mineral dyes, and which is occasionally used to this day, is lead sulphide, formed by the double decomposition method by precipitating a soluble lead salt with ammonium sulphide, or any other alkaline sulphide. By simply brushing an aqueous solution of lead acetate, also known as sugar of lead, on a white fur such as white hare or rabbit, a light, brownish coloration is obtained due to the combination of the lead with the sulphur of the hair. If the lead solution is carefully applied several times on this type of fur, until a sufficiently dark color is produced, it is possible to get a fairly good imitation of the stone marten. The brown color is very fast, being actually formed within the hair. In most cases, however, for dyeing lead sulphide shades it is necessary to use the two solutions. Thus the pale greyish or slightly brownish-grey shades of the lynx can be reproduced on white rabbit or hare by this process. A solution containing 60 grams of lead acetate per liter of water is brushed on to the hair of the fur which has previously been killed in the usual manner, and the hair is then dried. A solution of 50 grams of ammonium sulphide per liter of water is next brushed on, and the fur again dried. Care must be exercised in handling the ammonium sulphide as it is a very malodorous liquid, the fumes of which are poisonous when inhaled. The alternate brushings are repeated until the desired depth of shade is obtained. A very dark brown, approaching a black can be obtained in this way. This color can be used for the production of certain attractive effects. By brushing over the tips of the hair, which has previously been dyed a dark brown by means of the lead sulphide color, with a dilute solution of hydrochloric acid, or with peroxide of hydrogen, the hair will become white in the parts so treated, due to the formation of lead chloride or lead sulphate, respectively. Thus white tipped furs can be obtained, but the process is applicable only when the furs have been dyed by the lead sulphide method.
Potassium permanganate is occasionally used to produce dyeings of a brown shade on furs. Considerable care has to be taken in applying this substance, as it is possible to affect the hair. The strength of the solution must be varied according as the hair to be dyed is weak or strong. A cold solution of 10 to 20 grams of potassium permanganate per liter of water is brushed on to the hair, which is then dried. A brown precipitate of manganese is formed on the hair after a short time, and the process is repeated until the required shade is obtained. For furs with harder hair, stronger solutions can be used. The dyeing is very fast, but it is seldom used, cheaper and better shades being obtained in other ways. Spotted white effects can be produced on the brown dyeing with permanganate of potash by applying a solution of sodium bisulphite, the brown color being dissolved by this chemical.
The compounds of other metals, such as iron, copper, cobalt and nickel are not used in practise as the dyeings are not fast, and can be better produced in other ways.
CHAPTER XIII
FUR DYEING
Vegetable Dyes
With the exception of the few shades which could be produced solely by means of coloring matters of a chemical character, all dyeings on furs up to about thirty years ago were made with dye substances obtained from the vegetable kingdom, either alone, or in conjunction with the aforementioned mineral colors. The colors of vegetable origin used in comparatively recent times were mainly extracts of the wood of certain trees; so the name “wood dyes” has come to be applied generally to the dyes of this class. The use of the vegetable or natural dyes on furs dates back to quite ancient times, as frequent allusions and descriptions in Biblical and other contemporaneous literature testify. There are numerous pictures on monuments and tablets illustrating the dyeing of furs among the ancient Egyptians, the evidence indicating that the juice of certain berries, and extracts of certain leaves were used for the purpose. At a later period, in the Roman era, henna, which was used over two thousand years ago as to-day for the beautification of the hair of women, was also used to color fur skins. The instances cited here are merely of scientific and historical interest, and are not of practical importance as far as fur dyeing methods are concerned.
It was not until many centuries later that the dyeing of furs took on the aspects of a commercial art, and the substances then employed were chiefly tannin-containing materials such as gall-nuts and sumach, which in conjunction with certain metallic salts, particularly those of iron, were capable of producing dark shades. The use of iron compounds to form dark grey or black colors on leather tanned by means of the tannins, had been common for a long time, and it was natural that fur dyers should try to produce such shades on furs in a similar fashion. The use of the iron-tannin compound as a dye proved to be very effective, and to this day the production of blacks by means of the vegetable coloring matters has as a basis an iron-tannate. A formula in common use in the latter seventeenth and the eighteenth centuries for producing black shades on furs, is the following:
| Lime water | 1117 | parts |
| Gall-nuts | 1500 | „ |
| Litharge | 500 | „ |
| Salammoniac | 65 | „ |
| Alum | 128 | „ |
| Verdigris | 64 | „ |
| Antimony | 64 | „ |
| Minium | 32 | „ |
| Iron filings | 128 | „ |
| Green copperas | 384 | „ |
All these substances except the gall-nuts, the copperas and half the lime water were boiled up in a cauldron; then the gall-nuts and the copperas were placed in a bucket and the contents of the cauldron poured in, and the rest of the lime water added. The mixture was stirred up, allowed to settle for an hour, and when cool, was ready to be applied by the brush method. For dyeing by the dip process, a similar mixture was used, only considerably diluted with water. A study of the formula discloses the fact that in it are combined killing and mordanting substances as well as dyeing materials. The lime water, in conjunction with the salammoniac serves as a killing agent, the verdigris, copperas and alum are mordants, while the litharge and the minium, both compounds of lead, could possibly act as mineral dyes, and the iron filings and the antimony took virtually no part at all in the dyeing, except, perhaps to act in a mechanical way.