Prestige Optima and Boric Acid

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rkundla
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Prestige Optima and Boric Acid

Postby rkundla » Mon Jan 13, 2020 2:28 am

On my last cast, I tried to mix 1% by investment weight boric acid into a 38:100 mixture of Prestige Optima. The room temperature was approximate 64°F, so my investment water was at that temperature.

When I mixed it, the working time of the investment is usually 8-9 minutes, but it had dropped such that at 7 minutes it got really thick. I was in the process of vacuuming the flask when it got really sluggish. Unfortunately, my casting failed with poor surface quality. Not sure if it was a metal temperature problem or issues with degassing the investment, but that 1% of boric acid really messed up my typical flask investment timing.

I'd try it with 40:100 mix, which in Optima is pretty fluid, but I'd really hate to have it start to set up too quickly. Anybody else add boric acid to Optima and have good results?
Mikkopee
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Re: Prestige Optima and Boric Acid

Postby Mikkopee » Mon Jan 13, 2020 1:53 pm

rkundla wrote:On my last cast, I tried to mix 1% by investment weight boric acid into a 38:100 mixture of Prestige Optima. The room temperature was approximate 64°F, so my investment water was at that temperature.

When I mixed it, the working time of the investment is usually 8-9 minutes, but it had dropped such that at 7 minutes it got really thick. I was in the process of vacuuming the flask when it got really sluggish. Unfortunately, my casting failed with poor surface quality. Not sure if it was a metal temperature problem or issues with degassing the investment, but that 1% of boric acid really messed up my typical flask investment timing.

I'd try it with 40:100 mix, which in Optima is pretty fluid, but I'd really hate to have it start to set up too quickly. Anybody else add boric acid to Optima and have good results?

Why do you want to even use acid with Optima?
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sochin
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Re: Prestige Optima and Boric Acid

Postby sochin » Mon Jan 13, 2020 3:00 pm

rkundla wrote:Anybody else add boric acid to Optima and have good results?



Ron I use Omega + with 1.3% Boric premixed / dissolved into my distilled water.

**Edit 14/01/2020: so my percentage of Boric is to the water not the investment Ron. I add 13 grams to each litre of distilled water (think that works out at 1.3%?) and heat it gently until it dissolves properly then I cool it and refrigerate some of it. When it comes time to cast I prepare my water to temperature by mixing the water from the fridge with room temp until it is what I want.

I cannot imagine the Boric dissolving properly in the slurry at such a cold temperature if you just mix it with the investment. Try mixing Boric into cold water.

Safety warning is that you do not want to breath in any steam as you heat the Boric into the water. Breathing it in can make you sick. http://npic.orst.edu/factsheets/boricgen.html ***

For the temperature that my investment is at I find I need my water to be at 55°F to reach the optimal slurry mix for Omega + of 68°F.

Check the temperature of your slurry, see what is recommended for Optima ...... and you may be able to add colder water to the investment to lengthen the working time. Happy New Year.

cheers,
Sochin
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Jewelermdt
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Re: Prestige Optima and Boric Acid

Postby Jewelermdt » Tue Jan 14, 2020 3:51 am

Adding Boric Acid does reduce the time you have to invest. About 10%
rkundla
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Re: Prestige Optima and Boric Acid

Postby rkundla » Tue Jan 14, 2020 1:51 pm

Thanks Sochin for the info. I read online about someone who used 1% by investment weight, but they didn't say if they dissolved it in the water or not. I mixed it with the powder and then mixed it with my water. Everything looked fine for the first 5 minutes, then it started getting a little thick and then I realized it was setting up faster than I expected. ;)

I have a tank of RODI water I use for my saltwater aquarium, so my investment water comes from that tank at my basement temperature. If I mix my investment normally, I have plenty of working time up to the 8 minutes in the Optima spec.

Regards,
Ron
rsaldivar
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Re: Prestige Optima and Boric Acid

Postby rsaldivar » Tue Jan 14, 2020 10:56 pm

try adding the acid powder to the water and boiling it , make plenty for several castes , but keep it in frig so that it will be cold when you mix it , this should extend the work time more
wawatobi
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Re: Prestige Optima and Boric Acid

Postby wawatobi » Mon Jan 20, 2020 11:24 am

I use plasticast investment. I use 36 percent water to investment and mix one and thre quarters percent of the water weight boric acid. If I'm doing class rings with lettering on the surface I go up to 2.25 percent boric acid. use a high speed blender to mix the boric acid into the water. When mixing the investment, at the 3 minute mark I put approx. 5mm of water in the mix. That small amount of water makes the slurry less viscous. I mix under a vacuum. Get great results mst of the time.

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