Chrome Yellows, in a general way, are produced by the chemical combination of potassium chromate and lead acetate, or by digesting lead sulphate with a warm solution of potassium chromate.

The so-called standard shades are produced, varying somewhat in tone, according to the process of manufacture and the amount and nature of the adulteration contained.

They are distinguished as light, medium, and dark or lemon, orange and red chrome.

Alum, barytes and lead sulphate are used in preparing the lighter shades, and lead oxide for the dark or red chromes. In passing, it might be said that all chemical colors are subject to more or less adulteration.

This has become a fine art born of the necessity for cheap colors adaptable to the requirements of certain branches of the paint trade.

There are other methods of producing chrome yellows, which need not be entered into.

Chrome yellows are not permanent, but will rapidly deteriorate, unless protected by varnish; even then, they are uncertain. Other organic pigments affect them injuriously, and when subjected to the action of sulphurous gases they darken, as does white lead.

"When mixed with prussian blue, the latter color is, sooner or later, destroyed, a point well worth remembering.