Page:The chemistry of paints and painting.djvu/37

 underlying their art. Yet it would be unfair to the best colourmen of the present day to assume that they do not endeavour to provide, as far as possible, sound materials. But they do not manufacture all they sell. They are not paper-makers, nor, as a rule, are they manufacturers of oils and varnishes. Many of the pigments they furnish are not of their own make. If, for instance, you inquire the source of the artificial ultramarine you purchase of your colourman, you will find that it has probably been made in a factory wholly devoted to the manufacture of that pigment. The production of this material can indeed be properly carried on only in special establishments thoroughly equipped for a peculiar and difficult work. In reality, this specialization ought to be, and generally is, advantageous, but it renders the position of the colourman somewhat difficult. He has to assume responsibility for the soundness and genuineness of many products of the history and preparation of which he knows little or nothing.

This difficulty confronts him in many directions. I have known cases in which importers or manufacturers' travellers have offered to artists' colourmen speciously prepared but spurious pigments, such as madder carmine and rose madder made from artificial alizarin, ultramarine ash containing not a particle of the native lapis-lazuli, and a gold ochre owing its colour to a basic ferric sulphate instead of a hydrate. Then, too, some of the original localities of a few native earths, such as terre verte and raw umber, are practically exhausted, and most of the new sources yield products of inferior hue. Hence the temptation to 'exalt' the hue of the commercial article by some seductive though dangerous addition.

After these introductory observations, I may refer the