Refined oil is preferable to raw or boiled oil, as it will give the blue a clearer tone and appearance. As the percentage of silica and alumina, etc., in ultramarine blue does not figure much in the oil absorption for grinding the oil color, it is not necessary to go to the trouble of grinding specimen batches, as in the case of blacks, rubouts being sufficient for testing ultramarine blue.įor grinding ultramarine blue in oil for the trade the one that has the strongest staining power should be selected, and the average mixing will require two-thirds by weight of pigment to one-third by weight of linseed oil. One part of the dry blue mixed with 25 parts French zinc white, rubbed out to the utmost is the best guide for this. There being a dozen or so of grades listed, of which at least one-third will interest the color grinder for his various purposes, it is up to him to test samples offered him by the manufacturer for brilliancy of tone, shade, fineness, softness of texture, tinting power and clearness of tint produced with white. It is not our purpose here to extol any special brand or manufacture, but we must state that the brands manufactured in the United States are always preferred on comparison of quality and prices to those imported from abroad, excepting in rare instances, where extra brilliant, soft material is required and higher cost not considered. There was a time not so very long since when there was spirited competition and the makers of ultramarine sold the color at ruinous prices, but since the consolidation of interests both in this country and abroad the prices have gone up at least 75 per cent from those referred to. The better grades of soda ultramarine blue are preferred for bluing white pigments, because the whites so blued are not so apt to green off, especially when varnish is used in reducing the white for application with the brush or for dipping.Ĭolor grinders know what a large variety of grades ultramarine blues are offered in and how the selling prices of the dry blue differ, as well as the advance in the market prices of to-day, as compared with those of years ago.

The former is much paler in shade, the latter very much deeper. Soda ultramarine blue - Silica, Si02 - 40.8 per cent.

The better grades of ultramarine blue show average analysis as follows: - Sulphate ultramarine blue + Silica, Si02 - 48.5 per cent. The former shows more silica and less sulphur and sodium in an analysis, and when tested for tinting effect with white gives a clearer blue, less grayish tint, than the latter.

Sulphate ultramarine blue may be recognized by its having a slightly greenish- blue cast when ground in oil, while soda ultramarine blue has a violet-blue character.

Cobalt ultramarine