The scrap film and used hypo were incinerated leaving behind silver residue in the ash. This is not in use currently and has not been AFAIK for about 50 years.
The company I work for produces conductive circuits, membrane switches, etc. by screen printing conductive silver ink onto polyester film. Our silver printed waste goes for reclamation which is done by this incineration process.
"People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.