Ulrich;

In the US, a product called Steel Wool comes in 8 grades. It is dull gray and is produced as fine threads in various sizes according to these grades. It is sold in hardware stores. All of the grades appear to work in desilvering hypo. Another product comes as shiny ribbons as a kitchen product for cleaning pots and pans. It will not (AFAIK) work in hypo. It is sold in grocery stores.

PE