Yes. You need to dry the piece then break it into small bits and rehydrate by weight to the viscosity you want. Once it's throughly mixed, let it sit overnight to clear out the aeration. You will need to add flocculants to keep the slip in proper suspension when you cast with it.
Even orders as simple as a product you already make in a different color can go wrong. Always get at least half of the money up front and don't be afraid to charge through the nose. Better to give them a copy of your show schedule and tell them to see what you have next time.