Underwater Curing, why?

Today I did my first underwater curing with black resin and it turned grey which is kind of… meh?

Anyway… Reading through the Forums I saw a bunch of comments on that problem and how to prevent it which brings me to a question I should probably have asked before even trying the underwater curing method:

With an UV Oven like this one I made ( and shameless copy from the one in the Tutorial section ):

What is the actual benefit from curing under water? From my understanding it’s a timesaver only?
So instead of waiting for like 40min I’d only have to wait for like? 15min?

If some member of the community wants to correct me with their experience they’re welcome to, but I don’t think underwater curing helps at all. I have never heard of underwater curing nor do we tell anyone to do it, to my knowledge.

We do recommend that you cure Flexible underwater, but that’s because the water blocks oxygen, which inhibits the curing reaction: https://formlabs.com/support/materials/using-flexible-resin/

If you cure the part in water for like 5 minutes, it will cure the outside of the print making it not sticky, otherwise the oxygen can prevent the outside from curing as easily and while the inside might be cured the outside may still be sticky. But you really don’t need it curing in water all that long. Also note, if you have drops of water on the material before curing and you have the lights on, it will start curing where the drops are and leave drop marks on the model.

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Thats a really nice uv cabinet.

I might have missed the part that curing under water is being recommended for Flexible Resin only.

Thanks for clearing that up!

The more you know =)

I don’t even use water curing for the flexible resin. I just throw the part in the cure box after a quick rinse and let run for a bit.

After the cure is done use talc (baby powder) to soak up the sticky that’s left and rinse that off with IPA.

Your results may vary.

The reason for it is that Oxygen inhibits the resin from curing. It’s exactly how the CLIP no-peel-needed SLA print process works. The bottom of a CLIP resin tray is transparent to light and permeable to Oxygen. The Oxygen that oozes through prevents the resin from curing to the bottom of the tank so no peel is required.

In practice, in-water curing doesn’t appear to be absolutely necessary. I’ve tried it and it hasn’t seemed to make a lot of difference. But when I cure, I’m interested in curing the interior not just the surface. So I probably leave my prints in the UV long enough the surface ultimately cures anyway.

What makes it through the permeable layer in CLIP is 100% Oxygen. What’s in contact with one of our prints inside a curing box is only about 21% Oxygen. I’m guessing that’s why going to 95% Oxygen free in water (there is Oxygen dissolved in water) doesn’t make a huge difference.

I made my “budget UV curing jar” out of an acrylic jar so I could fill it with water. I never did a lot of prints with it, but I seem to remember that Flex resin turned almost black when cured in water but it stayed mostly clear when cured in free-air. And it did cure in free air. I don’t bother with water anymore.

In some materials it can be bad to cure with water because the material will absorb water

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