[GreenKeys] [die at dieconsulting.com: Re: [Bulk] Re: Telephoto machines?]

[David I. Emery]

On Mon, Jun 29, 2015 at 03:34:44PM -0500, Jim Haynes wrote:
> Western Union developed an electrosensitive recording paper in the 1930s, 
> which they named Teledeltos.  There was a black conductive inner layer, 
> with a metallic coating on the back and a grayish-white coating on the 
> front.  Supposedly it was electrically conductive all the way through, so 
> that a voltage applied across it would ablate the front coating to
> expose the black interior.  So maybe it wasn't necessary to spark, but
> sparking and smoke happened anyway.  As the ingredients were a secret
> one could worry whether it emitted toxic fumes.

	This stuff was common in some 1940s and 1950s military weather
fax machines - which used big sheets of it wrapped around a fairly large
drum.

	As I understood it, the coating on the front of the paper  was
mostly zinc oxide... with a carbon black impregnated paper backing.

	The stylus was thin tungsten wire which is very very hard and
resistant to high temperatures (needed to survive the arcing process).

	A machine I had used AC excitation... transformer coupled as I
remember it... 

	And indeed it did make smoke (and probably other toxic fumes)...
and also quite a bit of noise (the AC carrier frequency was clearly
audible).

	Any gray scale involved was very very limited at best... but it
did work OK for black and white weather maps...

-- 
  Dave Emery N1PRE/AE, die at dieconsulting.com  DIE Consulting, Weston, Mass 02493
"An empty zombie mind with a forlorn barely readable weatherbeaten
'For Rent' sign still vainly flapping outside on the weed encrusted pole - in 
celebration of what could have been, but wasn't and is not to be now either."