TV programme with Ian MacNaught Davies - teams identify old technology

There was a show a bit like Call my Bluff with various odditems with alternate descriptions of what they did, but I don't think its that one. Brian

I had one of those. I gifted it to the Science Museum. I used to take a lot longer than 30 seconds though. Simply getting the document properly focused on the camera's ground glass screen before putting the photo-sensitive plate in was a feat in itself.

Not something I have ever watched, so I can't help there.

I'm assuming that the time quoted was for the second and subsequent sheets, after the camera had been focussed for the first sheet - assuming the focus didn't change from one sheet to the next or one insertion of the photo-sensitive plate to the next.

I can't remember how they stopped the photo-sensitive plate from fogging as it was removed from the camera and inserted into the unit that sprayed toner onto it. It was a long time ago, I may have mis-remembered some of the fine details of the process as it was demonstrated on the programme.

What was the photocopying process that copied onto special paper with a matt finish that hurt your fingernails if they happened to rub over the surface, and which left an evil-tasting residue on your fingers after you'd handled the paper. I wonder if the paper was heat-, rather light-sensitive.

I remember at work we had a Versatec printer for printing circuit diagrams from the software that we used. This printed onto a continuous roll of special paper that was guillotined by the printer into page sizes. The paper smelled of paraffin and was slightly moist/greasy when it first emerged. I wonder if it had a print head that was n x 1 pixels across the full width of the paper, producing a pattern of dots at the pitch of the dots in one direction, and depending on firing rate and the speed of the paper in the direction at 90 degrees.

There would be no need to refocus the camera if you were making a series of copies at the same ratio. I think that the 1:1 original to copy ratio was marked on the camera slide. The operator would still have needed to be very quick though.

Essentially, it was a large bellows camera adapted from glass plate technology. The photo-sensitive plate was mounted in a wooden frame. After having an electrostatic charge applied, a metal screen was inserted into a slot at the end of the frame, so as to protect the plate from light after it had been taken out of the charger. A few plates could be made ready this way. The wooden frame was put into the camera, replacing the ground glass focusing plate, and the screen withdrawn, after which it was ready for exposure. After a few seconds' exposure, the screen was replaced and the frame taken out, to go into the toner tray. The screen was withdrawn a final time and a mix of tiny plastic beads and toner rolled back and forth on the plate. The paper was then, very carefully, laid onto the plate and the toner transferred by another electrostatic charge. Finally, the toner was fused to the paper with heat. Up to that point, there were multiple opportunities to smudge the image.

I rescued it from being tipped and its biggest use was converting drawings of an early railway locomotive to 1/2" to a foot scale for a model my father wanted to make in his spare time. The image in the bellows camera could be adjusted from 2:1 to 1:2 of the original and the image could be measured on the focusing screen, making it ideal for that. The original was lit by two light sources, one each side. I think each had 2 x 200w lamps, but it may have only been one in each. Either way, it made for quite a bright garage while they were on.

It was a long time ago, I may have mis-remembered

It was a complex process to remember when doing it regularly.

I don't recognise the description and I'm fairly sure I didn't taste my fingers after handing it, but special paper is something that thermal copies used. While the Xerox patents were still active, people tried a lot of different ways to make copiers that didn't infringe them.

I never came across that, but I did use a machine that produced real blueprints when I worked in a drawing office.

BTW, Google informs me that the programme was called 'It's Patently Obvious'

It's Patently Obvious

It looks as if I may have been thinking of the Thermofax technique.

I remember the variable print quality (writing/printing too pale, or else background too dark) and the curled paper.

At university they had a very unusual toner-type photocopier. Normally photocopiers move a light source across the original in sync with the rotation of the light-sensitive drum. This one exposed the whole original in a single xenon flash, so the light-sensitive plate must have been flat, not on a drum. It produced copies at a phenomenal rate: if you wanted multiple copies of a single original (so there wasn't the overhead of a sheet feeder) it could chuck them out at a rate of about 1 a second: I watched someone ahead of me in the queue printing posters. When I saw him dial in "100" into the number of copies, I thought "I'll be here all day waiting for this". That was in the mid 1980s. I've never seen another copier like it: all others have used a rotary drum and a scanning light.

Genome is your friend....

Is this him. A series is mentioned too.