Making a Positive Mold:
Dry the alginate impression and slowly fill it with labstone. You want to get into each crevice and be careful not to trap air in the impression. Gently tap the bottom of the tray as you fill so any trapped air bubbles will rise to the top. If you're using a Dental Base Former, fill that as well. If you're not using a Base Former just wait until the labstone thickens a bit and put a small pile of it on the table surface to form a base for your labstone positive. Wait some minutes until the labstone thickens a bit and then lay the filled impression tray upside down on top of the setting plaster form. Wait about an hour before you pull the alginate off. Plaster takes days to fully set, so you want to give it a little time to strengthen before you pull it apart. You now have a plaster positive of your teeth. File the edges down to make a smooth working cast.