Press-Molds are a great, simple way of converting a lot of models in a short period of time. In essence, a blob of putty is stuck onto a relatively flat surface and "pressed" with an indented tool. When the tool (or Mold) is removed, you are left with the reverse impression on the model.
Unfortunately I don't have step-by-step photos of how to create the mold, but it is fairly simple to describe. To create the mold, I used a piece of plastic tube from an old ball point pen. The edges of this were sanded to make it as "sharp" as possible. I stuck a pea-sized amount of Green Stuff epoxy putty inside. Think in reverse when carving the mold (The cast left by the mold will be the reverse of whatever you carve). To create the main dome of the boss I pressed in the back end of a paint brush. The rivet impressions were created with a toothpick.
Pictured here is the finished press-mold and a cast shield.
-To begin, I took some of the shields from the Dwarf Warrior box and filed away the emblems.
-Stick a small piece of putty on the shield and form it into a cone-like shape. This will aid in casting. The more of these you make, the easier it will be to estimate the size of piece you will need.
-Wet (or lick) the mold and press firmly against the shield. Any extra putty will ooze out the sides. If you sharpened the edges of the tube, it should "cut" the extra putty off and it will be easy to remove. If you get good at estimating the proper amount of putty to begin with, you won't have any waste to cut off.
-Carefully remove the mold, pulling it straight off the piece (not at an angle). Repeat as needed. I got these shields done in less than an hour.