334 PAINTS AND PAINTING 



while the Detroit Graphite Manufacturing Co., uses a mineral ore 

 with a large percentage of graphitic carbon in granulated form. On 

 account of the small specific gravity of the pigment, carbon and gra- 

 phite paints have a very large covering capacity. The thickness of the 

 coat is, however, correspondingly reduced. Boiled linseed oil should 

 always be used with carbon pigments. 



Mixing the Paint. The pigment should be finely ground and 

 should preferably be ground with the oil. The materials should be 

 bought from reliable dealers, and should be mixed as wanted. If it is 

 not possible to grind the paint, better results will usually be obtained 

 from hand mixed paints made of first class materials than from the 

 ordinary run of prepared paints that are supposed to have been ground. 

 Many ready mixed paints are sold for less than the price of linseed oil, 

 which makes it evident that little if any oil has been used in the paint. 

 The paint should be thinned with oil, or if necessary a small amount 

 of turpentine may be added; however turpentine is an adulterant and 

 should be used sparingly. Benzine, gasoline, etc., should never be used 

 in paints, as the paint dries without oxidizing and then rubs off like 

 chalk. 



Proportions. The proper proportions of pigment and oil required 

 to make a good paint varies with the different pigments, and the 

 methods of preparing the paint ; the heavier and the more finely ground 

 pigments require less oil than the lighter or coarsely ground while 

 ground paints require less oil than ordinary mixed paints. A common 

 rule for mixing paints ground in oil is to mix with each gallon of lin- 

 seed oil, dry pigment equal to three to four times the specific gravity 

 of the pigment, the weight of the pigment being given in pounds. This 

 rule gives the following weights of pigment per gallon of linseed oil: 

 white lead, 19 to 26 Ibs. ; red lead, 25 to 33 Ibs. ; zinc, 15 to 21 Ibs. ; iron 

 oxide, 15 to 20 Ibs. ; lampblack, 8 to 10 Ibs. ; graphite, 8 to 10 Ibs. The 

 weights of pigment used per gallon of oil varies about as follows : red 

 lead, 20 to 33 Ibs. ; iron oxide, 8 to 25 Ibs. ; graphite, 3 to 12 Ibs. 



Covering Capacity. The covering capacity of a paint depends 

 upon the uniformity and thickness of the coating ; the thinner the coat- 



