Slip is a watered down version of metal clay. You can buy slip or paste directly from the suppliers or make your own by adding water to a small lump of clay, filings or dried out clay. Slip can be used to attach two pieces of metal clay together, fill in small cracks or painted onto leaves, flowers, pods etc to make unique designs.
To make slip from scratch, you need a flat, non-porous surface like a piece of glass or plastic, a palette knife or spatular and some water. Take a small piece of metal clay and add a little water - spritzing it with a spray bottle works well.
Work the water into the clay using the palette knife. When the water is absorbed, add some more. Keep adding water and working it in until the clay forms a thick paste. Put it into a clean container - old style film canisters or small glass jam jars work well. You can add more water to the slip and mix with a plastic stirrer or a paint brush until it's the consistency you want.
Whenever you're filing your leather hard pieces, be sure to collect the filings. These can be added to your slip pot and mixed in.
Clay that has dried out can be reconstituted by cutting or grinding into small pieces and mixing with water. If the dried piece is quite large, you might want to make this into a lump of clay again. Otherwise, you can grind or chop it up and add to your slip pot. Make sure you mix in the ground up pieces very well before using in your designs.