Using Boric Acid to strengthen investment for resin casting

Jewelry Discussion
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I everyone. I make jewelry as a hobby and wanted to start casting resin 3d prints. What I don’t know is how boric acid should be used to strengthen investment (since resin has a tendency to expand a little during the burnout process). I had assumed that jewelrs will try to dilute boric acid in water by heating it up ahead of time. But I just saw a post somewhere that some resin jewelry casters simply mix boric acid and some calcium nitrate in the water immediately before mixing investment (no heated pre-solution)?

I will already be using a somewhat strong investment (R and R for white gold with the added fibers) but I would like to prevent any thermal expansion from the resin from destroying the quality of the surface.

Should I try just mixing 20 grams of boric acid powder and 20 grams of calcium nitrate to 1 liter of water right before mixing with my investment? That does sound nice and simple.

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One reason I ask is because if I go with the boiling the boric acid in water to make up the solution ahead of time… is it okay to throw the calcium nitrate powder into that water that I boil? Or do I add the calcium nitrate powder into the water only right before mixing into the investment?

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Mix 150 grams boric acid, (Hot Shot Roach Killer Powder), per gallon of deionized water in a jug and let sit overnight. It will dissolve without boiling at room temperature. Mix investment with this room temperature water. You can also add calcium nitrate if there’s a problem with ash, but castable resins don’t need it, nor do they need barrier liquid, in order for a clean burnout.

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Thank you so much!
Yeah the resin I will use is made for casting so thanks for the tip that calcium nitrate being added is not necessary.

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You can also buy investment specifically made for casting resin prints. Ransom and Randolph make one called Plasticast that works quite well.

To be honest though I’ve invested plenty of prints in just regular investment (just to get through it and not waste it) with little to no issues.

Different resins act differently though, and some expand more during burnout than others. The PowerResins Wax resin I use has very expansion.

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very “little” expansion ? What 3D printer are you using the the PowerResins Wax resin in?

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Sorry, yes, very little expansion (don’t know how I missed that :sweat_smile: )
We’ve got 4 printers going at the moment:

Anycubic Photon Mono SE
Anycubic Photon Mono X 6k
Anycubic Photon Ultra
Phrozen Sonic Mini 8k

The current workhorse is the phrozen. The 8k prints come out great!

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I pre-mix my investment water using a gallon jug filled with deionized water and adding 2% by weight (I think) of boric acid. My water does not need to be heated to get the required quantity of boric acid to dissolve.

I’ve given up on using calcium nitrate because I did not see a difference in the burnout quality except for some discoloration around the metal, most likely due to nitrogen dioxide permeating the investment. Having the right burnout cycle and combustion oxygen levels in the kiln/oven is more important than the benefit of calcium nitrate. Since four units of nitrogen dioxide, a known lung irritant, are released per unit of oxygen during decomposition, a quality ventilation setup is highly recommended.

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