Note - I'm working on getting all the stencils I've generated into a consistent format, as I do intend on posting them here! It could take a bit, but I wanted to get these shirts and the process post up this weekend. Also, I definitely don't own the original images, they're posted here only for illustration / education purposes.
These might be the last shirts for a while, been on a bit of a tear with them lately. The shirts used for these two (depicting Etched Oracle and Sheoldred, Whispering One) were Hanes Premium X-Temp V-necks, which yielded a more orange color when bleached. To not bury the lede too much, here are the final results!
Sheoldred completed shirt
Etched Monstrosity completed shirt
At this point I've settled into a workflow for generating designs from art, which breaks down into five steps -
Original art - Etched Monstrosity
First, isolate the subject. In GIMP I end up using the lasso-select tool and color-select tool as necessary to delete the background. This can take a while if the edges are hard to see, or if the subject blends slowly into the background, like Sheoldred does.
Second, create two new layers. The first is a block of black that fills the entire subject, providing a silhouette for later, but is kept "off" for the intermediate steps. Second, a "highlights" layer that sits at the very top of the stack for providing the "gaps" between pieces. These gaps create depth in the final design by allowing objects to pass behind each other, so it's important to grok how the original image is arranged.
Third, as the art on most cards is cropped by the frame, as need to expand the canvas enough to complete the figure. This usually means adding feet, tendrils, arms, etc. so the finished shirt doesn't have an artificial "frame" imposed on it.
Blocking layer with extensions
Fourth, and most time-consuming, adding the gaps. On the highlight layer I've settled on using 3-5px wide pencil and pen-curve tools to trace out the boundaries of each piece. Inevitably there's some iteration as I apply these at high zoom, and have to zoom out to make sure it all still parses at a distance.
Completed with highlights
Lastly, moving the file (usually in png format) over to Adobe Illustrator, to convert it all into paths. I fell into using the "black and white logo" setting on live trace as it has produced good results so far, but your mileage may vary. The only thing left to do at this point is to expend the resulting object into paths, un-group them, and delete the unnecessary segments. For me, this usually means retained islands of white. If kept, during cutting the laser will attempt to cut the boundary multiple times, isn't ideal.
For the cutter I'm using it expects vector cuts to be 0.01 pt black stroked paths, so I set everything to that and no fill color. I've also found that the speed-power-frequency settings needed to produce good results is about 80/5/2500, on a 150W cutter. After cutting the pieces of freezer paper are taken back home, and the host-shirt is laid out on an ironing board. After centering things up, I can start placing pieces and "gluing" them down with brief contact from a hot iron. Be sure to check you don't iron the wrong side of the paper, it WILL glue itself to your iron. Both of the patterns in this post took about 45-60 minutes to position all the fiddly pieces, tweezers were definitely a must. I've dropped an in-progress shot below.
Placing so many pieces
After it's all ironed down, a plastic poster-holder is slotted into the shirt to prevent bleed-through and bleaching of the back surface, and it's set outside either on the concrete or a protected work surface. I've settled on 4-6 fine sprays, quickly dabbing the excess off of the papered regions with a paper towel, followed by a five minute wait. I did that twice for each of these, followed by a minute or two agitating it a bucket of ice water to halt the bleaching. The water definitely turned orange. Lastly they were both thrown into the washer for a short cycle and dried. That's the whole thing!