There are lots of ways to make custom stamps, with varying degrees of difficulty. It's often a tradeoff of effort, cost and quality. This instructable demonstrates a process for using sugru and a laser-cut template to make stamps that can be highly detailed, with a minimum of effort.
Step 1: Mold Making
The first step to making a molded stamp is coming up with the mold. I used laser-etched 1/8" red acrylic. It's important that the mld be large enough to form any sugru that isn't part of the design, to keep it from picking up ink.
Every laser cutter uses a bit different software, so I haven't gone into detail as to how to set up and etch the design. If you don't have a a cutter of your own, you could always use an online service to make this part for you.
A few notes on design:
*Small details might get lost in translation, and will take extra care when removing the stamp from the mold.
* Use rounded, sans serif fonts to limit the finest details in the design.
* Don't cut the design too deeply. 1/16" is MORE than enough. The sugru is quite rigid when dry, so a little depth goes a long ways. Designs with less detail have more tolerance for deep cuts.
Step 2: Apply Mold Release
Apply a release agent to the mold. I used a commercially available release spray, but virtually any light lubricant should work fine. If I were to do it again, I'd probably use spray-on silicone.
Step 3: Open and Kneed Sugru
Sugru has a limited open time (the time before it starts to set up), so wait until you're ready to finish the process before you open the package.
Remove the Sugru, and kneed it into a flat piece, roughly the same shape as your stamp mold. I used an entire packet, because I didn't know how much I'd need, but I could have gotten away with less.
Don't worry about using too much, as it'll be forced out the edges, and easily trimmed. It's far more important to have a uniform piece than a particularly thin one.
Step 4: Apply Sugru to Mold
Gently press the Sugru onto the mold, making sure to cover the extents of the design. Don't worry about pressing it into every detail just yet.
Step 5: Add a Handle
To make the stamp easy to use, we'll add a handle to the back. I used a 2" block of wood, with the surface a bit roughed up, to ensure that the Sugru sticks to the block. Pick a block appropriate to the size of your stamp.
Press the block straight down onto the Sugru, preferably without any twisting or sliding that might shift the Sugru underneath.
Step 6: Clamp and Wait
Finally, clamp the stamp and mold together tightly, forcing the Sugru into all the nooks and crannies of your design. I've used a chunk of metal as a backer for the acrylic, but just about anything would work. The important part is to spread the pressure evenly.
Because there's not good airflow around the Sugru, curing might take longer than normal. In this example, I waited several days, and probably could have waited longer.
Step 7: Remove and Use
After you've waited as long as your patience will allow, you're ready to unmold the stamp. If you like, you can freeze the stamp-mold unit, to hopefully shrink the Sugru a bit, making the release process easier.
In any case, start from an edge and gently peel the stamp away. Avoid twisting or tearing to preserve the fine detail of your design.
Apply ink to your stamp with a regular stamp pad, and use. Notably, my stamp here is a bit defective, due to an issue with our laser cutter. Happy Stamping!