No. 6. DEPARTMENT OF AGRICULTURE. 333 



by mixing a large proportion of a white paint and a small quantity 

 of some highly colored paint or paints, thus producing the delicate 

 shades of color preferred for decorative purposes. It is clear, there- 

 fore, that so far at least as paints for wooden structures are con- 

 cerned, the white paints used as the bases for the various paints 

 are most important. Attention will therefore be confined chiefly 

 to them. The best known and most widely accepted white pigments 

 for making oil paints are Dutch-process white lead (a hydrated 

 lead carbonate) and zinc white, which is composed chiefly of zinc 

 oxid. The white lead is very heavy, flows very evenly from the 

 brush and has a very good body. However, it turns 3'ellow to black 

 when exposed to air containing sulfurretted hydrogen. It is sold 

 either dry or mixed with about 9 per cent, of raw oil. The so-called 

 pulp white leads contain considerable water, while they are said 

 to flow even better than the pure lead and oil mixture, but have 

 disadvantages as were above mentioned. Sublimed white lead is 

 quite different chemically from ordinary white lead, imparts high 

 body to the paint, is probably equal to the Dutch-process lead in 

 covering power and wearing quality, and besides does not blacken 

 like the latter. Zinc white, Chinese white, is lighter in weight than 

 either Dutch-process or sublimed white lead, is very permanent in 

 color, possesses a somewhat bluish tinge rather than the dreamy 

 white of the above mentioned lead pigments, but requires more 

 than twice as much linseed meal as they do to prepare a satisfac- 

 tory ''still paste," that is, the mixture of oil and pigment sold in 

 bulk for painters' use and requiring further admixtures of oil be- 

 fore the i}aint is ready for application. Zinc white has a better 

 covering power than Avhite lead, but is very deficient in body, so 

 that it is very commonly mixed with other materials to correct 

 this deficiency. 



Other white materials are very frequently substituted for the 

 high-grade pigments above mentioned. Among these may be men- 

 tioned lithophone, a mixture of barium sulfate, zinc sulfate and 

 zinc oxid. This is sometimes called sulfite of zinc white, another 

 similar pigment is Charlton Avhite. These materials are non-pois- 

 onous, do not discolor easily except when mixed with lead or 

 copper pigments, and have excellent body. Their own color is, 

 however, not uniform. At present they are employed chiefly for 

 inside use. Barium sulfate, commonly sold as barytes or blanc-fixe, 

 is very heavy and of low covering power; that is, has little body, 

 does not work well in. oil, works out streaky from the brush and 

 dries very slowly. Calcium carbonate sold as Paris white, English 

 white, whiting, etc., is a dull white powder which turns dirty grey 

 when mixed with oil, and requires a large amount of oil to mak? 

 a paste. Putty is simply a mixture of whitipg with 18 per cent, of 

 linseed oil. 



Calcium sulfate, mineral white, is rather transparent when mixed 

 with oil, but has a high covering power. 



White clay, China clay, has little body when mixed in oil. The 

 same is true of silver white, silex or silicia. 



Speaking of the pigments other than Avhite lead and zinc white, 

 Sabin, an authority on paints and varnishes, says of these, the 

 "barium paints are iho least objectionable, being in fact substances 

 chemically inert and of suitable composition; but they are practi- 



