Printing trials were not necessarily bad tests, since
oxidizing was usually added in these where it was necessary, and any
undeveloped coloring matter would thus be oxidized during the steaming
process: but, as he had stated before, it was essentially necessary in
such cases to have a fair idea of the amount of actual coloring matter
in the extract and to adjust the proportion of mordant accordingly.
Such trials should therefore be preceded by carefully conducted dyeing
trials with bichromate of potash. Mr. Thomson had raised the question
whether it would not be well for the manufacturer to prepare these
extracts in such a manner that they would contain all the coloring
matter in one condition only, in order to insure greater uniformity in
their quality and mode of application. This would, no doubt, be a
desirable step to take if the owners of dye and print works were more
in the habit of availing themselves of the service of competent
chemists experienced in this branch, for then they would be able to
make any extract do its full work irrespective of the state of
development of the coloring matter. Such, however, was not the case,
and it was a very common thing for the consumer of dyewood extracts to
require the manufacturer to prepare them specially for him so as to
suit his own dyeing recipes, or in other words to give exactly the
same shades, weight for weight, by his own method of dyeing as the
article he was in the habit of using.
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