The first stage is to mix up enough green stuff to cover a base. You make to make sure it is the right height and covers the base well. And leave to cure for about 10-20 minutes
This stage we mark on the design you want. At this point you don't want to drag the green stuff too much, it is possible that you will cause it to stretch and will warp your design. Once you are happy leave it to dry over night.
This is where the etching begins. Use a tool (I used a couple of my sculpting tools) to deepen the markings you made previously. They don't actually have to be that deep, just enough that the next stage will be effective.
Once you have etched in your design to the base, you then need to use something to make sure the mold will come free with minimal fuss. I used the below, Vaseline. Spread it over your base, making sure you get it into the gaps you have made.
Now, put another ball of green stuff onto your newly greased base. Push down to make sure it goes into the gaps, which is the important part. Push this down firmly, and leave to dry for about 10-15 minutes. I found it handy to make sure there is an edge on the stamp, it makes it easier to line it up in the following sections.
Once you remove the stamp, this is what you should have (but with your own design). Then leave to dry over night.
This stage is where once you've made the stamp you can just repeat to make multiple bases. I used milliput myself, but you can used green stuff just as well. Make a small amount of your material up and apply it to the base, much like the first step.
Take your stamp and push into the milliput firmly (first picture). Leave this for about 30 seconds or so, then carefully remove. Be careful not to drag or pull the stamp too much, this might cause the gaps it leaves to warp. (second picture) Then leave to dry over night. Once dry it will be available to paint.
In the end the bases should turn out something like this: