When I made the level-4 Menger sponge some time ago the problem was the old limit of 500k triangles. Later, printing 1mm holes on Transparent Detail was rejected (cleaning reasons) and the recommended size was 2mm holes (large and expensive). So the 0.3mm minimum walls of FUD material was the perfect excuse to print a level-4 Menger sponge with 0.3mm holes/walls (full model is 2.4 cm).
After the known delay of frosted orders, the model came but with an "Oops!" card saying that Shapeways were reprinting the model (not happy with the quality) and in the meantime I could made some post-production testing with the failed model. I think the fail was a fissure that were difficult to see. I had to make a little force to widen the fissure to see it and finally the model got halved. Meanwhile I had broken some of the 0.3mm walls with a toothbrush trying to remove the wax trapped in the 0.3mm holes. Another method I tried on one of the halves was a grease remover for kitchens (diluted in water a couple of minutes). Although it came a little less yellowish than the other half, I'm not sure if the FUD material is resistant to that cleaner (I'll try again during more time with the reprinted model).
And now the images, all after the toothbrushing and some of them after the halving.
In the last photo you can see the light through some of the cleaned holes.
Now I'm waiting for the reprinted model, that will be treated better than the failed one.