Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/426

418 as the atmosphere is very destructive to made glue. Never heat made glue in a pot that is subject to the direct heat of a fire or a lamp. All such methods of heating glue cannot be condemned in terms too severe. Do not use thick glue for veneering or joints. In all cases work it well into the wood, in a similar manner to what painters do with paint. Glue both surfaces of the work, except in cases of veneering. Never glue hot wood, as the hot wood will absorb all the water in the glue too suddenly, and leave only a very little residue.

Inert Pigments. An inert pigment is one which, when mixed with oil, will have no chemical action upon it. It will have no chemical effect upon any other substance with which it is mixed, as for instance barytes, silica and gypsum. On the other hand, white lead, Prussian blue, and chrome yellow, are chemical colors, and are supposed to chemically affect the oil and some other pigments.

Killing the Smell of Paint. Place a vessel of burning charcoal in the center of the room and throw on it two or three handfuls of juniper berries. Shut the windows and doors close. Twenty-four hours afterwards the door may be opened, when it will be found that the smell of the paint has disappeared. This can be done without any injury to curtains and tapestries.

Making Plaster Set Quickly or Slowly. In order to make plaster set quickly, mix it with water into which a little sulphate of potash has been dissolved. To make it set slowly, mix it with fine slaked lime. The time of setting may be regulated by changing the relative quantities.

Manganese. The various compounds of manganese are perhaps more used than any other driers. Of these the black manganese contains most oxygen, but many regard it as less useful than umber, which contains considerable manganese, and also iron. Umber is thought by some to make a less sensitive oil, that is, a fluid oil, or varnish, which changes less on exposure to the cold. Both