The Art of Dyeing — No. 12. Advice about Indigo and Woad Vats. Prussian or Royal Blue.

Scientific American 27, 17.3.1855

Advice about Indigo and Woad Vats.

There are many receipts which can be followed exactly in the art of dyeing, by persons who are unskilled, but this cannot be done in the management of blue vats. The skill of the eye, which can only be acquired experience, and likewise that of smelling, are necessary to manage such vats. And as they are very expensive, manufacturers should take heed to employ none but experienced persons to take charge of this branch of dyeing.

Within a few years past, the modes of dyeing Prussian blue on woolen goods in combination with tin and logwood, have been so improved, that such colors have (because they are very durable) superseded indigo colors on different kinds of woolen goods. — Receipts for these we will now present:


Prussian or Royal Blue
There are two ways of dyeing dark shades, first by bottoming, as it is technically termed, with logwood, and then dyeing with the prusslate of potash, or first dyeing with the prussiate and then topping with the logwood. Tho latter mode is the best.

For a dark blue, the goods do not require to be perfectly white, as the operation stripe off all old colors. To every pound of wool, which must be clean, two ounces of the prussiate of potash is put into the dye kettle along with two ounces of cream of tartar; add nitric and sulphuric acid until the liquor (after the tartar and prussiate is dissolved) tastes like glauber salts. The goods are then entered, if in pieces, they must be well selvedged or winched, and if yarn well turned, and the liquor in the dye kettle gradually brought up to the boiling point. The goods are then taken out and a little more sulphuric acid added. After the goods are boiled for twenty minutes or half an hour, a beautiful and rich sky blue will have been imparted to them. They are then taken out of the dye kettle, washed and hung up for a few moments to drip. Another dye kettle with a small quantity of logwood liquor, (say a pint of strength No. 3 in the hydrometer, for every pound of goods,) should be now boiling, to which add a wine glass full of the muriate of tin, stir well, and enter the goods. The kettle must be kept boiling for half an hour, when it will be found that a deep velvety richness will be imparted to the blue color, [] by adding a greater quantity of logwood with a proportional quantity of spirits (muriate of tin) a deep violet color will be the result. If some cochineal is used with logwood, a clear and beautiful crimson tinge is imparted to the good. This color may almost be considered permanent — it at least occupies more than a middle part in the scale, between the fugitive and permanent. From its exceeding clear and rich appearance, this color on goods has received the name of royal blue.

Coarse goods dyed by the above receipt, may be made a very deep blue by the greater quantity of logwood used, and if the goods were first of all prepared with a small quantity of the sulphate of iron — so much the better.

The chemical name of prussiate of potash is ferrocyanide or potash, a yellow salt (K2., Fe.3, N, C.2.) A richer and deeper blue will be given by running the goods through a weak solution of the nitrate of iron, and then washing them prior to operating in the prussiate bath. Hydrochloric or muriatic acid, if used instead of the sulphuric in the boiler, imparts a peculiar purple bloom.

Light blues are dyed without the use of logwood.

By employing about three pounds weight of logwood to the ten pounds of wool, and half a pound of the bichromate of potash — all in the earth kettle with the prussiate of potash and the spirits or salts of tin, a deep blue black will be produced resembling that produced in the pastel or indigo vat. It will not, however, stand exposure to the sun like indigo, but in other respects it is nearly as permanent.

For twenty pounds of wool, Smith says, three pounds of the prussiate of potash, and three quarts of nitro muriate of tin spirits are sufficient. These are placed in the dye kettle, the goods entered cold, and the liquer then brought speedily to a boll, and continued boiling for half an hour, when they are lifted, two pints of spirits added, and the boiling continued for some time longer. It must not be forgotten that the logwood is employed to deepen the blue, by simply forming a purple with the logwood and tin spirits. It in a color net difficult to dye by any person.