Professional Casters: Where do you get de-ionized water and how do you blow out flasks?

Hi everyone,

I’m about to start casting resin prints for the first time. They are much, much more finicky then wax models. Plus, I’m not professionally trained so I have 2 questions to any professional or experienced casters. I have had a lot of success casting wax models. But I do not want to leave anything to chance with resin models.

-Where do you get your de-ionized water from? I can’t find it so far so I was curious how you are finding it. It’s recommended by R and R for the Plasti-cast investment (and maybe all of their investments).

My second question is blowing out the ash inside the flasks. (Resin prints, even if fully cured, probably produce ash) I don’t own a large air compressor. I was thinking of using one of those dust cans but the plastic stray would melt if too close.

Is there another way to blow out a flask if you don’t have a large, metal air compressor nozzle? Some people go really high on burn out to reduce ash but most investments are not made to go super duper high so I think it’s safer to blow out with compressed air after holding the burn out at 1350 for an hour or two.

de-ionized water, don’t they have that at Whole Foods in their dispense water by the gallon device?
regular, alkaline, and de -ionized. bring your own bottle

thanks for that tip, unfortunately, the nearest Whole Foods is very, very far away for me.
But…other stores have similar machines so you gave me an idea to try and look for that. I think some of the Publix’s have a machine like that and even Lowes.

Yeah but on the shelves…I think Publix (I’m in Florida) and Walmart only carry distilled and reverse osmosis water.

Reverse Osmosis water only means they don’t do the extra step of De-ionization which removes oxygen and salts. The best water to cast with is De-ionized according to R and R. It’s SUPER hard to find to me. I might give up for now and try RO only but I hate leaving things to chance. I read online that some people have to find fish stores who sell de-ionized. I’ll try a few more places.

Distilled is the best water to use. Available at any grocery store. Don’t worry about de-ionized. They are suggesting you use water that has no contaminates rom your tap water.


Hi Rick, RO water does actually remove salts, it just does it with reverse osmosis membranes and not with a resin bed. That is why it doesn’t need de-ionization, because the membranes do that already. In fact RO water probably removes more “stuff” in general from the water than deionizing. I am a chemist by day and spent the first part of my chemist career learning water chemistry. I am by no means an expert anymore though. Hope you can find what you need.


Wow, I’m glad you posted here, thanks!

That is so confusing to me though. If Reverse Osmosis water is better (or Distilled is fine as the other poster suggests), then why is there “lab grade deionized water” available for purchase I see online and it’s very expensive, like 14 dollars a gallon. And I believe the Reef Aquarium stores sell deionized water because people who build delicate saltwater reefs need the purest of water and they only use deionized I believe. I totally think you know better than an average aquairum person but why does R & R recommend deionized and the reef aquairum phanatics? Just curious why the confusion (that I have too).

Does de-ionization remove more salts and oxygen than RO alone? I wonder if R and R think that’s important for the investment, not just the lack of mineral deposits.

Yeah I think I’ll just try Distilled first. Curing the resin models is more critical I believe.

It really depends on the membranes that are used for RO water. They can vary. When I worked in the lab we took the buidling deionized water and ran it through another RO purification system to get the clean water we needed for lab work. I suspect deionization has been around for ever and that is what has been used and so that is the knowledge that has carried through to today. Experiment and see what works for you. To answer if one is better than the other, you would really need to see the specifications of the deionization or RO system that is used as they can vary. Good luck.


Nothing beats distilled if it actually is distilled.
Distillation means it has been boiled and the vapours condensed to liquid again.
This is what is used for medical injections, dialysis and such.
RO and Deionized are for the most parts the same.
Most proper RO systems have deionizing filters as part of their setup.
If you want a deionized system to last you better add an RO system first.

But why they need super clean water I really do not know.

I cast with resin prints as my main production method. The most critical part of the process is making sure the prints are 100% cured. It’s also very important to use an investment made for plastics, like R&R Plasticast. The resins need to be held at 1350°C for a while to de-ash the mold, and make sure you blow some compressed air into the flask right before pouring.

A tip for sprueing - red sprue wax doesn’t stick to resin prints well, so I use white sticky wax as a transition to make for stronger trees.


I hate casting resin prints because the burn out cycle is inconveniently long and the results are inconsistent.

I buy resin models printed in a high temp resin. Sand the models gently and then mold them in regular mold rubber.

Good luck

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My husband works at a platinum foundry.
They ionize their own water in house. And yes deionized water is different from distilled. Distilled just has impurities removed. And this from Aquasana… “Deionized water, also called deionised water, DI water, or demineralized water — is water that has had ions removed. Ions are molecules with a positive or negative electrical charge. In water, they appear as dissolved mineral salts. Minerals commonly found in tap water include calcium, magnesium, iron, sodium, chloride, sulfates, nitrates, carbonates, and silica.” Tim says that they put their deionized water in the fridge to chill before mixing the investment. It’s important in large scale casting to make sure that the water temp is consistent. Both the water and the investment are very carefully weighed. Since they do platinum casting the deionized water is important so that the platinum is not contaminated with other minerals. Car washes use deionized water to reduce spotting
As for removing the ash use a shop vac.
Good luck -Jo


Unless you are talking about a “brand” or product group, distillation is the purest you can get.
The water is then boiled and the vapors are condensed in a column and collected.
This removes ions, organics and non ionized particles at a much higher level than any de ionization can do.

Distilling is the oldest method to de-ionize water. Salt ions do not generally boil off during the process; they stay behind in the boiling container. Deionized just means deionized by not-distilling. It can be with mixed-bed resins or RO. “Lab grade” only means one of two things: they actually measure the conductivity of the water (since no method gets rid of 100% of impurities, be they ions or not), or they don’t and they are just taking your money. When I was a researcher there was some sense of pride in achieving water with a resistivity of 10 megaohms or such, but this was fairly silly, since we had previously used a still with rubber tubing, and that water was fine for the most delicate molecular procedures. My wife and I just bought a home distiller to get water for our humidifier, ironing, and silversmithing. It was not expensive, got here fast, has a small footprint and works great. No running to the store to get “good” water!


Thanks, everyone.

I used distilled water and my resin casts came out pretty darn good for my fist time.


I had clean, smooth surface on about 90-95% of the models’ surfaces and the only bad surface quality that I had I think was more from having too hot of a flask for sterling silver.

(I pull the flask when it’s 950 because I think it takes me a while to vacuum cast to get the crucilble metled) But I think the flask was well over 800 when I poured so I think that is the only reason about 10% had some rough surface.)

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One alternative to owning a compressor is to buy an auxiliary air tank, which you can fill periodically at a gas station. You’ll still need a hose and blow nozzle though.

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Hi Rick, so many years ago when I was casting Wow. It was early seventies then and plain water was about as complicated as it got but with a twist. We found that we had a much better vacume result if we left the water bucket to stand in air for twenty four hours. There was much less bubbles (boiling) when we vacumed out the flasks.

buy distilled water at Walmart in gallon jugs… cheaper than other alternatives. The distinction between the purity of highly deionized water and distilled is trivial in terms of removing mineral salts which ionize in water. Triple distilled is very pure and very expensive and only used for laboratory purposes, unnecessary for household use nor for what you are doing… if you had good results using the cheapest alternative, go with it.
Grocery store bought bottled water is not mineral free. Water is treated by reverse osmosis, removing dissolved salts, which leaves it tasteless…some salts such as bicarbonate are then re-added for flavor.

If another concern is dissolved oxygen in the water (i.e. air), distilled water should not have dissolved gases in it as boiling drives off the air and other dissolved gases… the bubbles that form in a pot before it comes to a boil is the dissolved gases, mostly all air that is being driven out by heating.

Sorry, I’m not believing the part about those little bubbles being dissolved gasses somehow undissolving with heat. If anything, heat increases the ability of a liquid to dissolve things, doesn’t it? Wouldn’t a more plausible explanation of those little bubbles be that they are composed of water vapor, which get larger as the heat increases and the boiling begins? I suppose one could conduct an experiment, with one pot containing regular water and the other containing distilled water, and see if the latter boils without forming small bubbles first.