I have been collecting sandings, scraps, old paste, hard nodules that were dropped, and recovered silver from the bottom of the water bowls etc, from every brand of Fine Silver clay over the last 12 years. I have tried to reconstitute it in the past by grinding it to a fine powder, sifting the cat hairs and other stuff out of it and adding a bit of water. It did not hold together as there was very little binder left in the mix.
 

Here is the coffee grinder I got at the thrift store and the jar of about 5 ounces of powder I ground and sifted

There was a conversation about this on the Metal Clay Europe Facebook Page and someone mentioned methylcellulose works a bit, but I never heard how well. I was looking around on Amazon.com one day, and found this bottle of Psyllium husks for my old kitty to help with her constipation.

I ordered it and when it came in I mixed it in water to see how potent it was before I fed the cat any. 1tsp adsorbed a lot of water and it was a smooth gel. That had me thinking about the silver powder I had stored.
So I experimented and this is what I found:
(this is US measurements)
One slightly heaping teaspoon of old fine silver powder
1/16th tsp of Psyllium powder
about 35 drops of water +/-
Mix on a piece of plastic with a small flat knife until well mixed and it is starting to hold together. You should be able to either roll it into a ball and mix well in your hand or put into a plastic report sheet and roll and fold till well mixed. Wrap and put into a container overnight and the next day it should be ready to use.
If your clay is totally unknown as to what types of fine silver went into it, then I would fire it at
1650F for at least an hour.

I will be firing this piece in my next hot load of silver and will be enameling on it. Stay tuned for the final product. I am so excited to be able to use all this reclaimed silver I have been collecting!
​Please leave a comment as to your success with this. Thanks