First of all, I cannot take credit for this fabulous idea. It belongs to The Polka Dot Closet. Visit her post here. It is very detailed. I cannot believe I have never seen this before! It is a great way to cut down costs and what DIYer doesn't have plaster of paris?
Start off by picking up some clay that will stay soft so you can reuse it.
Find some items you could use to press into the clay to make a mold. Before you press it into the mold she suggests using dusting powder to prevent sticking. I didn't have any of that, so I just used flour. Here I used a flower knob, but I also used a finial top and a drawer handle.
Mix up some plaster and spread it into the molds, tap to get rid of bubbles. Make sure to smooth out the top so you will have a flat surface (not shown in this picture).
Wait for them to dry then carefully pull the mold away. You may have to sand some of the edges, but for very thick areas you want to get rid of a dremel works well.
Come back tomorrow to see what I use one of these for!