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  #1  
Old 06-01-2019, 05:05 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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Casting

Since we seem to discuss other things than blowing these days, can you remove casting plaster from the glass with acid say?
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Old 06-03-2019, 09:57 AM
Shawn Everette Shawn Everette is offline
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Water and a brush should be sufficient. The internets don't really have a definitive answer on acids, and some are suggesting using an alkali instead.
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Old 06-03-2019, 11:03 AM
Eben Horton Eben Horton is online now
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If it is small, an ultrasonic cleaning bath works wonders
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Old 06-03-2019, 11:03 AM
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A water pick dental cleaner works great too
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Old 06-03-2019, 09:15 PM
Peter Bowles Peter Bowles is offline
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Coca Cola!
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Old 06-05-2019, 06:21 AM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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Thanks for suggestions- I wonder if the lack of a clear solution on the net is because there simply isent a good way to do it?
I was thinking bigger than what would fit in a ultrasonic cleaner- are there large ones?
If a waterpik will do it how about a pressure washer? Is there a way to add pumice to the spray after the nozzle?
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Old 06-05-2019, 07:51 AM
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How about the .25 cent car wash? They'll love you for it.
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Old 06-05-2019, 08:35 AM
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Quote:
Originally Posted by Michael Ahlefeldt-Laurvig View Post
Thanks for suggestions- I wonder if the lack of a clear solution on the net is because there simply isent a good way to do it?
I was thinking bigger than what would fit in a ultrasonic cleaner- are there large ones?
If a waterpik will do it how about a pressure washer? Is there a way to add pumice to the spray after the nozzle?
Investigate soda blasting. You own a boat... in the US, marinas soda blast the bottoms of boats to remove the soft antifouling paint down to the gelcoat layer.

I think each person who casts has their own ways.
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Old 06-05-2019, 10:18 AM
Shawn Everette Shawn Everette is offline
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From what I've read the plaster is not readily reactive, so mechanical force tends to be the best option. Some have suggested light acids or bases, but that's been surface coat removal, not casting devestment.
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Old 06-05-2019, 11:52 AM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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Well coca cola would be a weak acid
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Old 06-05-2019, 12:12 PM
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Tons of info on the web. Citric acid, Vinegar, Lemon juice, Muriatic acid all will dissolve plaster over time. Sodium citrate used in beverages as a flavoring additive has been used in the dental industry for removing plaster. 15 percent sodium citrate to water.
Plaster and stone remover seems like it would be my first choice. Jsp makes some and it is easily found on amazon.

I knew plaster had to be fairly easy to dissolve with acid but this did make me do a little reading. Questions like this are why I come here. Even if I never get into casting the knowledge I gain is valuable to me for growth. Thank you
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Old 06-05-2019, 12:15 PM
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Soda blasting sounds promising. Iím very impressed by the results Iíve seen for applications when delicate items need to be cleaned. I saw paint and graffiti removed from soft carved stone that I thought would be destroyed. I look forward to hearing the end results.
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Old 06-05-2019, 12:30 PM
Shawn Everette Shawn Everette is offline
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Were you able to find something on the more scientific or professional site? Or just the same hobbyist "just use vinegar" reddit stuff I did?

While not technically a pro site this is the closest thing I could find that attempted to be scientific about it, https://www.physicsforums.com/thread...-paris.139990/
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Old 06-05-2019, 04:24 PM
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I have used CLR on occasion to loosen investment from hollow core castings. Turns it to snot that you just pour out.

I've not used it for the application in question, but it may be worth a try. I always have some around the house that I use to clean our shower doors.
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Old 06-05-2019, 06:24 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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How about that? After ok halfheartedly searching and reading about this to and from for some years, and repeatedly sort of giving up on the fact that its like Eben says- people do it different ways, just says that people dont know how to do it.So Shawn points at a link that has a person actually testing a whole lot of acids at different concentrations at different temperatures and it turns out it is not acid at all but baking soda that works- thats non intuitive in my book. Thanks Shawn. A day or two on craftweb eh?
So the question begs to be asked if caustic soda is better? Is that what you are talking about Greg?
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Old 06-05-2019, 06:59 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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Ill look into soda blasting, never heard of it�� my boat is steel, aluminum oxide when needed��
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Old 06-06-2019, 01:09 AM
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Quote:
Originally Posted by Shawn Everette View Post
Were you able to find something on the more scientific or professional site? Or just the same hobbyist "just use vinegar" reddit stuff I did?

While not technically a pro site this is the closest thing I could find that attempted to be scientific about it, https://www.physicsforums.com/thread...-paris.139990/
This was the only link I still had open in my browser. I can try and find more of the info I found but it seems you have looked into more then myself. I do appreciate the good info.

https://www.quora.com/How-do-I-turn-...c7cf00c09ff214
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Old 06-06-2019, 08:18 AM
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Keep in mind what those chemicals actually are. Caustic Soda is sodium hydroxide (lye) and is indeed corrosive . It will go right after your soft tissues. While it does in fact come as beads, protection of yourself and your surroundings is important. It's neutralized with Boric acid or ammonium chloride.

Muriatic acid is 70% hydrochloric acid. It does fume to a degree. It is neutralized with sodium salts. That nice name doesn't make it less corrosive.

Probably best to remove as much casting plaster as possible before relying on dissolution. It also would depend on just what plaster you're actully using. Disposing of the sludge would I imagine be an issue as well if anyone found out you were doing that.
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Old 06-06-2019, 09:56 AM
Shawn Everette Shawn Everette is offline
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I didn't see that particular quora, but that does to look to go with the same base answer. I generally have a hard time trusting sites where people can anonymously post information. I'm actually surprised there's not more definitive answers, but mechanical removal has always worked for me.
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Old 06-06-2019, 10:05 AM
Shawn Everette Shawn Everette is offline
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The main ingredient in clr is actually lactic acid, not a base like caustic soda(sodium hydroxide).
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Old 06-10-2019, 03:23 PM
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Quote:
Originally Posted by Michael Ahlefeldt-Laurvig View Post
So the question begs to be asked if caustic soda is better? Is that what you are talking about Greg?
From the link to wiki page:

"Calcium Lime Rust, more commonly known as CLR, is a household cleaning product used for dissolving stains, such as calcium, lime, and iron oxide deposits.

Its ingredients may include various compounds:[1][2]

water
lactic acid
gluconic acid
lauramine oxide
Propylene Glycol
n-Butyl Ether
Glycolic acid
Sulfamic acid
Disodium Capryloamphodipropionate
Ethylene Glycol n-Butyl Ether
Citric Acid

One formulation is Lactic Acid 12-18%wt, Gluconic Acid 2.50-3.75%wt, Lauramine Oxide 1.50-3.25%wt with the remainer being water. [3] The product also contained phosphoric acid at one time,[citation needed] but it is now phosphate-free."

It's all about acids. I haven't looked at Shawn's offering on "physics forum" but I imagine it's better than all of our anecdotal "advice."

As far as vinegar goes, the business compound is acetic acid. If you want more of a punch try looking to lab supply companies for higher concentration as vinegar is only around 4%.

https://www.labsupplyoutlaws.com/che...lacial-lab.htm

My own thoughts on this are that sticking is often caused by the glass being too hot, and fusing with the silica in the investment. You may be able to remove the foreign matter stuck to the surface, but there will still be a blemish. In other words there is no chemical fix for this, and coldwork will still be necessary.

I know Pete gets nervous when discussion turns to strong acids- with good reason. I never recommend anyone turn to hazardous materials unless you really know what you are doing.
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Old 06-10-2019, 04:17 PM
Michael Ahlefeldt-Laurvig Michael Ahlefeldt-Laurvig is offline
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Well the point made in the link Shawn posted was that its not acid that works- its baking soda, the opposite of acid. So that said, caustc soda is mean base stuff, would it work better? Im not a bit concerened of the dire warnings that is always mentioned, the whole concept of making glass is nasty things all the time, its stating the obvious.
And yes Greg I agree, it may be neccesary to cold work things left by themold material , but Im talking about getting rid of it to start with
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Old 06-10-2019, 04:28 PM
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Well, sodium hydroxide is not the same thing as sodium bicarbonate. One you can brush your teeth with or belch really loudly. Some people commit suicide with the other.

I may have to try Liquid Plumbr in the future.

I've switched to this stuff for opening drains. Works the best:

https://www.oatey.com/2377177/Produc...-Glug-Crystals
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Old 06-10-2019, 05:29 PM
Shawn Everette Shawn Everette is offline
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The interesting thing that I was noticing about the clr was the inclusion of several surfactants to the mixture, about half the list. I'm imagining some are being used to put the ether in solution, but the others could be accelerating the solvent reaction.
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Old 06-10-2019, 06:01 PM
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At the house, we use sodium b carbonate when we've burned the bottom of a cooking utensile. It works, albeit slowly.

Calcium or sodium hydroxide which is in concrete is not something you want slopping into your boot unless you like deconstructive surgery.
My points are usually around the notion that the genral community is really not well schooled in hazardous materials at all, so, I remain a loud noise urging caution.

I once neutralized a batch of Ammonium bifluoride in an etching booth with soda ash. It virtually jumped out of the booth at me straight sideways. At another point I neutralized sodium bromide at a poolside restaurant in the fire service. That time? I added silica to just cool the reaction down. No heroics. That worked just fine.

Try to keep in mind whatever you do may wind up in the landfill. Sometimes the injuries come days later.
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