A Treatise on Calico Printing, VOL. I-II
Printed for C. O'Brien, Bookseller, Islington, and fold by Bew, Paternoster-row: Richardson, Royal Exchange: Murray, Fleet-Street: And the Booksellers of Manchester, Glasgow, Dublin, &c.
1792
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* Using paste or gum occasionally as thicknings, or vehicles for carrying them to the cloth.
(58) Vinegar distilled from verdigrease; but to speak of this as well as other articles, new terms of doctrine mut be used, at present deemed incompatibl.
As vinegar dissolves iron slowly, and only then with access of air, the tar acid, or more properly the acid of wood, has been lately much used and extolled, being applied immediately to the calx.
(59) The perfect digestion of galls and other astringents; or their saturation with their solvents, is as fully needful in certain courses; for in both cases, the extreme division of tin particles produces the best effects.
(60) The latest modern opinion is that the cloth itself in the copper undergoes a partial solution.
Iron-liquor, or calx of iron dissolved in vinegar, from whatever liquor procured, is the agent for obtaining permanent black from madder; and by judicions tempering with water forms purples and laylocks;* the black itself being only a deep purple: — With logwood a less permanent black or purple, of a bluish duskier hue is obtainable. With weld and other yellow colouring substances, the hue is brown. When added to the red colour, or more properly the aluminous solution, then chocolate, pompadour, blossom &c. are formed in the madder copper, according to the proportions of mixture, from the colouring matter being taken in combination by both the calx of iron and the earth of allum at the same time.
Some think the additament of alder bark, or decoctions of other astringents might help the iron liquor in certain cases, as when newly prepared or procured by a weak acid.
Of the tar acid iron liquor, or the chalybeat one, the writer will say little; the expedition of procuring either may have its advantages, but much caution is needful before a course of work is attempted with them, unless the manufacturers are of undeniable repute: for though a deal may be said of the acid employed and of its immediate operation on the previously prepared calx, yet every printer, as already observed, is fully sensible of the value of good old iron liquor, and of course preserves it for particular purposes.
As to what is said by some as the acid procured from cyder, perry, &c and using steel filings, it still is but vinegar, and the steel must be converted into a calx before a drop of iron, liquor can be formed. Hence the only superiority it can boast over any other, is in its being fre-er in its first stages of manufacturing from useless or injurious matters; and from the iron being very minutely divided, and, of course, presenting more surfaces to the action of the acid, the solution is more expeditiously performed.
It may not be irrelavent to add, that the more concentrated the vinegar, or the nearer it approaches to distilled or radical vinegar (58) it may be proportionably effective, both in respect so power and expedition: and small beer or weak wines are known to give of little power. As to the age of common iron liquor, that is, such as is procured in the old way, it is indisputable that the particles of iron or its calx are found to cause a finer colour and of being more uniformly dispersed, however lowered the mixture may be, than in the new iron liquors. In fact, it is this perfect saturation, and the case is applicable to aluminous and other solutions, that denotes its excellency. And this is no where more evident (as well as with the red colour) than in the Changing of copper-plates, wherethe engraving is very fine: for it is certain that the colour made at different grounds by different operators, will not suit the same engraving. Other circumstances to be sure may intervene, yet the above is certainly one worth attending to (59) But in this instance it may be said in one case, that, by the particles of iron being more saturated with the liquor, and in the other by the earth of allum being completely saturated with the vinegar, of course, both the calx of iron and the earth of allum are carried with their solvents into the finest interstices.
N. B. With blue colour for copper-plate printing the difficulty is greatest: hence the colour here cannot be too pure and free from adventitious matters, not only for filling the in terstices, but also for the sake of the doctor or clearer.
Perhaps what tearers call vittry colour, or that which in boiling, or other stages of preparing black, appears frothy, scummy, lumpy, Ice. is from the iron liquor not being free from plumbago (which is a combination of the base of fixed air or pure charcoal with iron. Of which much might be said, but for reasons just given, it is waved at present, except that being black lead, it is insoluble in acids.
In the copper a decomposition of the liquor takes place either by attriction (note 28) or by an attraction of the colouring matter of the madder, or else by an attraction of the cloth itself (60) to the calx held in union by the vinegar: which in this case is similar to the earth, of allum in combination with vinegar.
The writer will not yet pretend to say how the foxing of the purples (a common phrase) may be avoided with little trouble, but he oblerves as it is sure to take place if the water be heated to a certain degree, it renders the purple an iron mould, or a metallic stain; the combustion having decomposed it, and seperated the colouring matter from it. For here be it observed that the purple on the cloth is a compound matter, formed of the calx of iron and the colouring matter of the madder.
Why the red is not so easily decomposed is from the closer attraction of the colouring mat ter of the madder with the earth of allum: and it has been observed, the black and consequently the purple is deemed only a deposition of the calx; besides, as a proof of it, it is known that the deeper the purple, the easier it is affected, which only seems so from there being mere substance to be acted on.
In maddering if the heat be too intense, a similar circumstance happens, that is, a browness ensues, so likewise does it in mere welding; only in the first case the colouring substance already on the cloth is changed, but here the colouring matter of the weld in the copper is changed, combustion being the cause of both.
Note An iron liquor, not generally known, is obtainable from a decoction of rice in which red hot iron is thrown; it is then to be added to a certain quantity of vinegar in which red hot iron has likewise been thrown.
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