TWELFTH ANNUAL YEAR BOOK— PART X 509 



weather conditions, a larger amount of thinner may be used than for 

 outside work. Also, paint for inside work should dry faster than one 

 for the outside, and a somewhat larger amount of japan drier is gener- 

 ally used. 



PAINTING OF METAL. 



Tin or other metal roofiner, also galvanized iron such as gutters and 

 rain spouts, are very difficult to paint, as often the paint does not stick 

 well. This is probably due to a very thin film of grease left on such ma- 

 terial from the process of manufacture, and before attempting to paint 

 a tin roof it is best to scrub it perfectly clean with soap and water or 

 with cloths moistened with benzin, and then thoroughly dry before apply- 

 ing the paint. Galvanized iron may be treated in the same way, but it 

 is much better to let this material stand for some time exposed to the 

 weather before painting. The metal portions of machinery are generally 

 cast iron or steel; wrought iron is rarely used, thoueh it is more durable 

 than steel. Cast iron is not so liable to rust as steel, and also the pieces 

 are frequently thicker than the steel portions of a machine. There is 

 perhaps nothing that actually needs paint for protection as much as the 

 steel and iron portions of machinery. Before painting such material 

 the greatest care should be taken to get the surface perfectly clean. Do 

 not apply paint over rust, but clean thoroughly down to the bare metal 

 with scrapers or wire brushes, and finally with dry scrubbing brushes. 

 It is a mistake to spare labor in preparing a metal surface for paint. 

 All oil and grease should be scrupulously removed, and the metal surface 

 should be absolutely clean and dry before painting. The paint should be 

 well brushed on, carefully filling all cracks. 



Two or three coats of any good paint may be used. The paint which 

 is generally sunposed to protect iron from rusting better than any other 

 is red lead. This is expensive, however, and rather hard to apply. The 

 color also is some objection, althoup^h this can be overcome by mixing 

 some dark pigment with it. The addition of a small amount of lamp- 

 black improves the color and the working quality of red-lead paint. A 

 paint made of basic chromate of lead (so-called scarlet lead chromate, 

 or American vermillion) is even better than red lead as a material for 

 protecting iron. This also is very expensive, even more so than red lead, 

 and while the protection is not so complete with the use of cheaper 

 paints made of iron oxid pigments, on account of the fact that pieces of 

 machinery are very likely to have the paint scratched and injured me- 

 chanically, it is perhaps best to use an iron oxid paint for most of such 

 work, because of its cheapness. Any eood oil paint will give valuable pro- 

 tection to iron if it is properly applied. 



MIXING PAINTS. 



Paints may be prepared either by mixing the dry pigments with oil and 

 turpentine or benzin; or the paste pigments may be used. The latter 

 are ground in a small amount of vehicle, generally linseed oil. The best 

 pigments are exceedingly fine powders, and it is frequently a matter of 



