|From UK cinema, scratched-in slide for double feature (c. 1956)|
|British scratched-in slide for (c. 1944)|
Custom slides could also be quickly fabricated in order to flash an immediate message to the screen.
Film historian Kevin Brownlow recently related a personal anecdote in an email which illustrates the point. I'm sure he wouldn't mind if I shared it here:
|British scratched-in slide (c. 1956)|
"When I was a few months old, my parents went to the local cinema in Crowborough, Sussex, leaving my aunt looking after me. I must have sensed what was going on, because I roared so furiously that my aunt had to telephone the cinema and they projected a slide (over the film - sacrilege!) with handwritten lettering saying 'Would Mrs Brownlow please return to Kevin.' So I had my name on the screen at six months."
Projectionists had several different processes by for laying their message on glass, all of which essentially boil to two different approaches.
The first approach is to simply take an appropriately sized pane of glass and write on it using ink, paint, or grease pencil. When projected, the resulting image is a white background with black or colored text. This technique is described in the 1915 manual, A Guide to Kinematography (Projection Section) for Managers, Manager Operators, and Operators of Kinema Theatres by Colin N. Bennett.
|Hand written slide for St. Louis Great Western Grain Company (c. 1910)|
"Simply paint or write on the clear glass. For painting, any opaque mixture will serve. Light red or ultramarine blue water colour paints are good, and the glass can easily be cleaned off again. To write in words with a pen, use a ball-pointed or broad-pointed nib and a mixture of ordinary writing ink and ultramarine blue of the consistency of very thin paste. Electric lamp lacquer (white spirit varnish coloured with alcohol soluble aniline dye) may be flowed over the uncoated side of the announcement slides to introduce colour and make them less glaring on the screen."
|Ad typed on cellophane then sandwiched between glass panes, Seattle (c. 1920)|
This process had the advantage that the projected image appeared on the screen as light against a dark background instead of the other way around. Another advantage was that the scratched out areas could be covered by a color wash, thus affording the opportunity for multicolor text and embellishment.
Returning to Bennett's manual, he describes the Preparation of Scratched-in Announcement Slides":
"Cover a clean 3 ¼ inch square of glass [note the standard British slide dimension] with any opaque coating that can be scratched off in fine lines with a sharp pointed instrument, such as a sharpened knitting needle, or a darning needle stuck for support in a cork, leaving the point jutting out half an inch. White, or light green, Hall's water distemper is a simple announcement slide coating..." Bennett then continues to recite half a dozen alternatives for uniformly coating the glass, and then concludes "...the finest possible lines can then be cleanly made. The wording of all scratched-in announcement slides projects white on a dark background."
This "Scratched-In" process apparently later became quite popular, so much so that a British company, Morgans's Slides Limited, developed pre-coated blank slides and sold them under the trade name MORROPAQUE. The coating on these slides was pre-ruled with very fine lines to assist the exhibitor in aligning their written text. The coating also easily accepted color dye, so that that exhibitors could creatively color them as well.
|MORROPAQUE slide and the resulting projected image|