378 APPLIED SCIENCE 



423. Zinc Bases. Zinc compounds are often used as a 

 basis instead of lead, when the paint is to be exposed to 

 fumes of sulphur compounds. Zinc does not mix as readily 

 nor does it have the same body as lead. 



424. Ocher. Ocher. made with iron oxide as a base, is usu- 

 ally used to cover iron. The color varies from a brown to a red. 



425. Staining, Filling, and Varnishing. Dyes dissolved 

 in water, oil, or spirits are applied to the bare wood to give 

 color and to bring out the grain. This process is called stain- 

 ing. Another method of staining is to expose the surface to 

 ammonia fumes in a closed receptacle. The fumes by chemi- 

 cal action will in this case turn the wood nut brown. 



The pores of the natural or stained wood are filled with 

 liquid or paste filler, liquid fillers being used on close-grained 

 woods, such as pine, and on large surfaces, and paste fillers 

 on coarse-grained woods, such as oak or chestnut. The 

 coat of filler is applied evenly, allowed to stand 24 hrs., and 

 then sandpapered lightly. In fine cabinet work on close- 

 grained wood, white shellac is often used as a filler, since 

 shellac makes a good foundation and does not darken the 

 wood as does varnish. 



The best paste fillers are made of ground rock-crystal 

 mixed with raw linseed oil, japan, turpentine, and some 

 color suitable for the wood. They are applied to the surface, 

 worked into the pores, and left on the wood in a thin layer. 

 When the filler has become dull and chalkish, it is rubbed off. 

 The rubbing is done first across the grain to fill the pores 

 thoroughly, and then with the grain to bring out the high 

 lights. Twenty-four hours are allowed for the filler to hard- 

 en. One application is usually sufficient. 



