454 WHITE IMAGE SCREENS [Cn. XII 



usually in the general exhibition room, and there is no special 

 boxing or enclosure of the apparatus. But in moving picture 

 theaters, where there is some danger from the inflammability of the 

 picture films, both the fire underwriters and the municipal regula- 

 tions usually require some form of fire-proof operating room. 



IMAGE SCREEN 



621. Next in importance to a suitable room for exhibitions 

 with projection apparatus is a good screen upon which to project 

 the image. 



No one has ever more briefly and clearly stated the qualities of a 

 good image screen than Goring & Pritchard: "It should reflect 

 the greatest -possible quantity of light and absorb the least." 

 "Every care should be taken to render the surface as smooth, white 

 and opaque as it can be made" . . . "inasmuch as the bril- 

 liancy and perfectness of the picture will greatly depend on the 

 whiteness, and the sharpness of its outline upon the smoothness of 

 the screen." The screen should be dull white, never shiny. 



622. Screens of plaster paris upon the wall. A screen ful- 

 filling all the requirements just given is a wall coated with a smooth 

 finish of pure, fine plaster of Paris. 



623. Painted wall screen. While a plaster of Paris wall 

 screen is perhaps the best, a smoothly plastered wall, if properly 

 painted, gives almost as good results and is much cheaper. The 

 wall, as stated, should be finished as smoothly as possible by the 

 plasterers, then it is coated with pure linseed oil if porous, or with 

 a mixture of equal parts of linseed oil and turpentine if the wall is 

 hard and non-porous. When this is dry, the wall is painted with 

 either white lead ground in oil and thinned with turpentine, or 

 with "sanitary paint" thinned with turpentine. The sanitary 

 paint has the advantage that it does not turn yellow with age, and 

 that it is more easily cleaned with soap and water. 



When the paint is properly thinned it should be strained through 

 one or two layers of gauze (cheese cloth) to get out any lumps or 

 coarse particles. 



