Does Dark Build Plate on an SLA Printer Reduce Exposure Bleeding?

In one of the recent posts I printer a solder paste stencil. The print is challenging as it contains small details, is thin and prints directly on the build plate. Even I use the same exposure on the first layers as did on the other layers, the first layer showed some exposure bleeding.

The hypothesis is that the silver surface of the build plate reflects the light, which cures the resin, and therefore more resing gets cured. I was thinking about getting really dark black paint and to paint the build plate. One of my readers, Zemerick (thank you!), brought up that Vantablack cannot be used (as it is a fragile forest of carbon nanotube), but Black 2.0 or 3.0 is just acrylic paint with a lot of pigment. So I got Black 3.0 and painted half of my build plate:

Half of the build plate painted by Black 3.0

The paint can get be scratched easily (you can see the test scratches), so I was afraid it would peel of. To my surprise – it didn’t. But the test print didn’t stick to painted plate:

The first test print

Reason for that? The paint is soluble in resin. I got leaking black pigment to my vat, the paint after a 5-minute print was really soft. I tried 2 more prints with roughly the same result.

Since the prints peel off, there is not much to compare and I cannot say if it helped or not.

Conclusion? None. I still think UV absorbent surface finish on the build mitigates the exposure bleeding. However, I am not sure how to create one. Anodizing would stick but is still too reflective. I could use spray paint, but not sure if it is dark enough and if resin will stick to it. I probably wait until the replacement build plate will be available and then (maybe) try some more experiments.

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