Magic Metal Paper

In the seventies, Casio created the FP-10 printer for the fx-602p.

It could also be used on other calculators like the fx-502p and fx-702p. Like the ZX Spectrum printer it  was a spark printer that used metallised paper. This paper is no longer available, at least anywhere I can find. I managed to get a printer for a reasonable price, and it came with one roll of paper. The paper appears to be a layer of metal at the front (aluminium I assume), then a black layer of some kind and then a paper backing. The rolls are very narrow and only a couple of metres or so long. I only have one roll of paper so I decided to see if I could make some paper to use on the printer.

I measured the paper and got a figure of around 3 to 6 ohms per square (very rough measure).

That's a printout from an fx502p, which doesn't ordinarily have any real alphanumeric capability, but the printout does. The printout is very clear.

Attempt One

Aluminium foil. I tried aluminium foil in the printer. This didn't work as the foil doesn't have the physical strength to get driven through the mechanism.

Attempt Two

Stiffen it up. I glued foil to paper to try to give it a bit of stiffness. This also didn't work. The foil tore and I suspect there was no electrical contact between the foil and the metal plate at the front that forms a circuit between the paper and the electronics.

Attempt Three

Try to find conductive paint to spray on some paper. There are conductive paints but they are very very expensive and I didn't try those. I also inquired about silver spray paint that looked like it was conductive. There's no metal in it apparently and it is not conductive.

Attempt Four

I find that there is a conductive paper available. It's called 'teledeltos' and it is used for science experiments and I believe was also used in fax machines many years ago. I bought some (not cheap) and it arrived as a large roll. It appears to be totally unsuitable as it is carbon based and the conductive side of the paper is the wrong side to work in the printer. The resistance of this paper is probably too high anyway at 2000-3000 ohms.

The black side is conductive, but you'd want to print on the white, non conductive side to get contrast. I tried scraping some of the white off so there's contact with the metal plate on the front of the printer, but no sparks at all. 

Attempt Five

I tried shiny aluminiumized paper based on a plastic sheet backing. This was conductive on one side but again wouldn't print.

Attempt Six

This involved aluminium 'gilding' foil. This is very thin foil that you can glue to paper (or other surfaces). It results in a shiny silvery effect. I used spray glue to attach the foil to paper as it will not adhere on it's own.

When I measured the gilded paper I got a figure around 0-1 ohms so this is much more in the ball park of the original paper. When I cut strips and ran them through the printer, there were some sparks, but not enough to get a printout.

 I'm not sure why not as the resistance seems similar to the original paper. The texture is different though, with the original paper a grey matt surface and the gilded paper much shinier.

Here's a selection of papers that I tried:

That's gilded paper on the left, shiny aluminiumized paper in the middle and the magic original paper on the right.

I also cut some original paper at a shallow angle so the layers become more apparent:

You can see the backing layer of paper, then a black layer and finally the aluminium on top. The black provides a contrast after the metal has been sparked away, I think.

Conclusion

There must be some magic employed in the original paper. It's not just that it is conductive, as none of these conductive 'papers' worked at all. The things I can think of are maybe:

• The resistance of the paper is critical to operation. None of the resistances were exactly what the original paper showed, either much higher or slightly lower.
• The texture of the paper is important. The original paper has a distinctive matt finish. If you scratch it with your fingernail then you get a metallic shine, so there's aluminium there.
• The thickness of the paper is critical. I doubt the papers I made are exactly the same thickness as the original.
• The printer has been finely tuned to print on just the original paper. maybe it can be re-tuned to print on other 'papers'.

I'm not sure what to do next. I may have a look inside the printer and see if there's some clues in there.