I know a lot of people create custom brushes in PS, but this technique is a little different (and technically not a "brush")  in that it uses the custom shape tool so brushes are resolution independent, and can scale in real time to different shapes and sizes. It is fantastic for blocking out paintings really quickly. I'll use the painting on the left of Big Wing, the main character in my animation "Little Wings", as the example. Hopefully this is helpful to you. If not, here is a video of a raccoon stealing cat food. If you do end up using this, I'd love to see what you create!

1. First I create a black painting, in this case it's a really knarly vine that I want to use as foliage. There really aren't any limits with this other than keeping it black, so feel free to go ape shit, detail is cheap. The painting is on it's own layer so it can easily be selected.

2. Select your painted layer and then the "Paths" tab. Down at the bottom of the paths tab is a little dotted line icon that kind of looks like Princess Leia. Click that to create a "work path".

3. With the work path highlighted, go to: Edit> Define Custom Shape. Give your Custom Shape a cool name and save it.

4.  Type: "U" to bring up your shape tool (or you can select it in your tool palette like an old timer) and make sure you have "fill pixels" turned on in the tool settings, and "custom shape tool" selected (it looks like a wonky star). From there you can select your new custom shape from the drop down and paint away!

After trying to model tiny parts with traditional sculpting tools and continually messing them up, breaking them, and calling them dirty names, I decided 3D printing would be the way to go. 
Each piece had to be part of a working puppet rig and the hero puppets will be about 12 inches tall so strength, fidelity, and an accurate representation of original drawings were all things that were really important to me.

I used a Cube3D printer (2nd generation) and right out of the box I printed a few models that were included that turned out pretty well. With the factory models I was looking for limitations in the printing process because I knew they were designed to look good, and once you start printing custom models, any imperfections or shortcomings are going to be amplified. Kind of like the magnifying mirrors people use to pop zits. The thing is, I love imperfections. I think they give pathos to what might otherwise be a cold lifeless thing. I just want to have as much control over them as possible so that I don't get halfway through a shot and have my puppet break in the middle of it. 

The 3 things I noticed were:

1. The Cube has a hard time with cantilevers. Holes, dangly things, arms...These were going to have to be modeled with support structures.

2. The "smart" supports that the cube software uses are super janky. As is usually the case with any technology that carries the "smart" moniker, it isn't. It's not that they didn't try, it's impressive that with the click of a button Cube will throw in supports so your model doesn't look like a Dali painting. I just find that when I'm modeling, I'm going to know where the supports belong better than the software and I can reduce a lot of excess flashing and print goobers.

3. The printer is loud, slow, fussy, and totally awesome. When you're printing, half the time it sounds like it's burning out motors, and the other half it sounds like a super badass aphex twin song.

My 3D experience is mostly in Maya and Zbrush and I knew I would be using a pipeline that involves Drawing>Maya>Cube Software>Printer. The cube uses a proprietary file format (.cube) but the software will accept stereo lithography file types (.stl) which is more standard, although Maya doesn't natively support .stl so  I found a great .stl exporter plugin called multitool (here) and after a little tooling (converting maya units to inches, installing the .mel script...) I got a successful .stl export from Maya. I brought the .stl into the cube software, prepped it for printing, exported a .cube file and printed! The results are above, note that I shot the print with a coat of primer before I took a picture so it's a little hard to see, but it's looking pretty good!