The educational screen (c1922-c1956])

362 The Educational Screen Lantern and Slide Conducted by Dr. Carlos E. Cummings The editor of this department will attempt to answer all queries submitted, on the making or projection of lantern slides, lanterns or still projectors, or pictures made by photography for educational purposes. AH matters connected with moving picture projection or films will be discussed on another page. All readers of the Educational Screen are invited to make use of this page, and submit questions on any topic properly considered herein. Some Common Faults in Lantern Slides THE standard lantern slide as adopted in this country is 3^4 by 4" in size. As far as we know, every lantern manufactured in the United States will accommodate a transparency of these dimensions. The manufacturers as a rule are very careful in cutting the plates and as this is a matter beyond the reach of the lantern slide maker, cannot be controlled in any way by him. There is very little fault to be found with most of the slide plates on the market. Coated on thin glass free from bubbles and uniform in size, they occupy practically the same position in the plate holders, making it possible for us to depend on our ground glass marking for centering. The best cover glasses are secured by cleaning up spoiled and obsolete slides, but this supply is seldom sufficient where our work reaches proportions of any magnitude. The covers which we buy in bulk will usually average 90% of bubble-free glass. Old negatives if sufficiently thin can be cut into good cover glass but we must avoid those of any great thickness, as a thick cover results in a heavy bulk and possibly a greater likelihood of breakage in the lantern. Our friends across the water prefer a slide 3J/2" square and some American lanterns are prepared to take this size in addition to the standard. It is better, however, when the opportunity offers to build up these small slides to standard size. We have used two methods to accomplish this. The slides can be lengthened by attaching to each end with binding strips a piece of cardboard about the thickness of the slide and .3^ by ^^ in size. A sticker on both sides will usually produce a sufficiently strong joint to withstand ordinary wear. Another method which gives us the advantage of producing a more uniform appearing result and also of .inserting our own mats consists in opening the slide, discarding the cover, and attach ing to the positive two pieces of glass 3% by ^" by means of gum strips on the face. This is then remounted with a standard size cover and when finished appears uniform with other slides and allows full space underneath the cover for whatever labels we wish to place thereon. While slides too thick to be placed in the ordinary carrier are unusual, nevertheless they are sometimes seen, and a slide too thick to be projected is of no more value than no slide at all. The matter of matting is one to which unfortunately too little attention is often given. The mat serves as a frame for the picture on the screen and also to carry the maker's name, title, etc., preventing this data from being removed or obliterated by handling. Mats can be purchased in quite a variety of openings but most dealers use a round cornered opening about 2}^ by 3" as standard. A round corner on any form of picture is an abomination and the use of such openings is more or less of a habit. It is undoubtedly easier to manufacture a die which will cut a round cornered opening than to produce a similar die which will cut a square corner, and it is true that where the lantern is not set square with the screen, a round cornered picture does not appear as distorted as a square one. Small cutout patterns of metal can be secured by means of which openings can be cut with a small wheel cutter but great care should be taken in using these cutters to secure a clean, sharp edge, free from fuzz or fiber. A plate of glass affords a suitable surface on which to cut but it has a tendency to dull the cutting wheel. A piece of thick zinc which can be procured of a photo engraver gives greater freedom from slipping and is not so hard on the cutter. Where conditions permit, each slide should be matted individually to produce the best effect. A pat-^