Making colors.

Scientific American 16, 6.1.1849

We have tested these receipts and found them to be correct and good. They will only answer on wool and silk, or both combined. For cashmere delaines they are the grand desiratum. A French color makers have recently arrived in this country to execute these colors in some of our print works. THey are given to our readers as peculiarly valuable for that branch of business. The stuffs will be all the better to made a little stronger than is defined in the specification - so we have found in testing them. $2000 was paid for the receipts about two month ago y an eminent Calico Printing Establishment near this city.

The coloring matters hitherto employed in printing textile fabrics composed of wool, of silk, and of wool and silk combined, are usually in the state of extracts which are obtained by aqueous solutions from various kinds of dyewoods, and from other substances, such as orchil, cochineal &c., and by evaporating more or less, these extracts. But it often occurs that using boiling water to extract these coloring matters, several other soluble substances are extracted alog with them, so that when an aqueous solution of any coloring matter is evaporated, the residum retains a great deal of these extraneous substances, and therefore produces colors, less brilliant than if it were isolated and pure. All aqueous solutions, particularly highly concentrated ones, deposit in the course of time the whole of the coloring matter which is in the state of suspension, and likewise, in the majority of cases, a resinous substance, which has probably mixed up with it a portion of the coloring matter. And as the concentration or strength of the extract diminishes in proportion as the deposit increases, it follows that the liquor in any two vats must always vary more or less in strength, according as one may have stood longer than the other. Now such differeces of intensity cause irregularity in the printing of goods; and there are still greater differences caused by these extracts not having equal affinities for water, and consequently some have a greater tendency than others to absorb steam, from which causes combined steam printing (le vaporisage), is rendered an operation extremely uncertain in its effects and very liable to accidents. This process has been known by the name of dry dyeing (teinture seche) which wrongfully implies that water is not necessary, which however is not the case, for all manufacturers are careful to keep their goods moist which they wish to fix with the colors, either by placing them in a humid atmosphere or by damping them during the process of steaming, by opening the steam cosk a little at the commencement of the operation, so that the steam which escapes may be condensed upon the goods and thereby impart to them the proper degree of humidity. Without these precautions the colors would be feeble and spotty in appearance, unless, indeed the colors can be previously rendered equally lygrometric, which it is an extremely difficult thing to effect. If two pieces of the same printing fabric are subitted to the process of steaming, one very dry and the other very damp, the color of the first will be spotted and feeble, while the second will be bright and full bodied. All printed woolen oods, with the exception of those which are printed with colors, which like the French Blue, have a great afinity for water, require in order to fix firmly the color, to have condensed upon them the largest possible quantity of steam, wither before or during the process of steaming but without the quantity being so large as to allow of running (coulage) and if should happen that in the same piece, and by one and the same operation, the color runs in one part, is weak in another, or is clear and decided in a third, it must arise from the piece not having in all parts an equal affinity for water.

To remedy the various inconveniences arising from the use of extract in steam dyeing, (vaporisage) it is necessary to replace those extracts by preparations in which the coloring matters are in a purer and more unalterable state and which are suck that they may be fixed in the goods in an uniform manner, and at a desgree of humidity as analagous as possible to that of the dyeing bath; and this is what has been effected by the following processes.

These improvements are founded on the general fact, that if to a decoction of any coloring matter, there be added a salt, such as the chloride of tin, the base of which has a great affinity for the coloring matter, an insoluble precipitate is the result, which holds very little, if an extraneous soluble matter, and contains the coloring principle in a state of much greater purity than the ordinary extracts.

Although such an extract is insoluble yet it is capable of combining perfectly with the textile fabrics aforsaid provided that the drying be performed while the goods are well damped. In consequence of the insolubility of this precipitate, the color obtained by means of it, may be fixed by a steam without previous dissication, and goods which may have been dried after printing may be again wetted without the danger of the colors running. The precipitates which may be thus obtained and applied, are numerous, but as they are all very similar in effect, it may suffice to specify only those whuch appear to be most susceptible of general use.

(To be concluded)

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