Casting With Alginate

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Twitchfmx8811

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This kinda an off question so I thought id throw in in the noob forum. Can you make a mold with alginate and then cast out of it with more alginate. A friend of mine wants to make a rubber copy of his hand. Ive looked around online and the only thing ive been able to come up with is Platsil Gel 10 and the smallest amount we can find is 2 lbs for almost 30 bucks. The local hobby stores have mold making kits but it has plaster and he wants rubber. Can I used brush on mold making rubber or some alginate and just use it for a cast?





oh and btw. Hey guys long time no see.
 
If I were you I would look in to getting some dragon skin from smooth-on and using a flesh tone pigment so it looks like skin but that can get kind of pricey. Here is a tutorial on how to make fake hands for cheap Linky! Also check out this tutorial as well they have some very useful tips Linky2! Hope this helps.



And welcome back!
 
You could make a plaster mold of the hand using a home-made plaster recipe. It's usually just some flour and water with a bit of school glue. Then, use the plaster mold to cast in whatever rubber you want. Since it's plaster, there might be a few inconsistencies, but that's the easiest and cheapest way I can think of to do it.
 
Well the mold itself is no problem. The question im having is can i use regular alginate for the CAST. Since rubber from smooth on is almost $40 after shipping.
 
Alginate is made from a plant, and the mold only has a short life (something like 24hr) because it has to stay moist and deforms over time. So while it's probably technically possible to make a mold and casting from alginate, you wouldn't want to, and couldn't keep it very long. Smooth-On makes several products intended for creating molds of body parts. Whatever you do, you would be unwise to use most common mold making materials, because they will cause heat and chemical burns if applied directly to the skin.
 
Honestly, I'm not sure about that. If it was me, I'd do a test piece with a release agent to see if it's possible. Don't want to ruin the mold. However you find to pull this off, let us know. That should be useful in the future.
 
Burns? We are talking about the same stuff the dentist puts in you mouth to take casts of your teeth. And the same stuff that comes in life cast kits for making plaster casts of your babys hands and feet. Dont think I need to worry about burns. But I wasnt sure how long the stuff lasts. I was looking at a box of alginate and depending on how you mix it depends on how strong it is. ie such and such makes it good for one pull and such and such is good for 3 or 4. Im just wondering if I were to get a small box of alginate and one tub of the brush on rubber and make the mold with alginate and then using the brush on rubber and just pour it into the mold if that would work.
 
TwitchFMX8811 said:
Burns? We are talking about the same stuff the dentist puts in you mouth to take casts of your teeth.



Sorry, I didn't state it clearly, and you misunderstood. No, alginate will not burn you, and that is why they use it. Alginate is pretty much the only mold-making material that you can safely put inside your body. And that is why dentists use it, but the price for being non-toxic is that the life of the mold is terrible. An alginate mold must be used to make a casting within a few hours, and is totally useless in just a day or two. It also tears really easy, kind of like Jello but a bit tougher, maybe scrambled eggs.



Most "real" mold making materials, ones that are not alginate, will cause chemical or thermal burns. Plaster generates a lot of heat while setting, and usually can only be used on flesh if laid on in thin bandages, not poured on. (Plaster is made by baking the water out because the heat brakes the bond, and then when the water is reintroduced the that bond-breaking energy is released as they reform.)



You best bet is probably to make an alginate mold of your hand, then quickly make a plaster casting. The alginate mold will likely be destroyed, because getting fingers out is tough [compared to teeth for example], but the plaster casting is pretty tough. You can then use the plaster casting to make a permanent mold, from a more permanent material than alginate, to make lots more hands. I would suggest silicone, like MoldMax Stroke from Smooth-On with a support shell, but you could use latex rubber too.
 
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Well alginate would work fine. He only wants one. Its not like we are going to mass produce his hand in rubber. I just need to know if I could use maybe the brush on rubber and just pour it into the mold to cast it. He doesnt want to spend $40 on liquid rubber from smooth on. I have the mold down im talking about the CAST.
 
I don't think you can cast any type of latex rubber in alginate at all, brush on or pour in. Latex is liquified by a solvent, which needs to evaporate out in order to solidify. Alginate is powder and water, so it's wet. Latex isn't going to dry at all inside the wet alginate mold.



You need to use either a gypsum based material that hardens in the presence of water (like plaster or dental cement), or possibly some type of chemically curing material that actually hardens, and isn't inhibited by the presence of water (like epoxy resin maybe). You can't even use polyurethane casting materials (like the Smooth-On casting materials most people use), because polyurethane is extremely sensitive to moisture.



If your buddy is worried about $40 being too much, you're really backing yourself into a corner. This stuff simply isn't cheap (not $10-20 cheap, anyways). Is there something else you could do, that might not be as good as rubber, but work for your needs? Maybe make do with plaster, or maybe wax? I'm trying to think of something else, but can't really come up with anything.



EDIT: I poked around online and couldn't find much of anything to suggest you could cast rubber in an alginate mold. You're tiny budget makes it really tough. One thing I thought of, you could maybe make a wax mold of your hand, instead of alginate. I've done it before, but you'd probably have to get creative to avoid spending much money on wax, because you typically do it in about 2qt of melted wax which is going to bring you right back up to spending money. The advantage of the wax mold would be that you could cast inside it with latex, in multiple thin layers (which would take forever, because you'd probably need 20 coats, each taking several hours to dry). Keep in mind that if you try casting inside wax with something that generates heat though (plaster, polyurethane, etc.) you might melt the mold, even if you cooled it from the outside with ice water.
 
Hmmm, I don't know if it will work but you can thin down some silicon caulking. The 100% silicon stuff. Normally silicon won't dry if it is thick because it needs water to swap out the acid inside however you can add some plain old acrylic paint to the mix and get a full tube to cure in minutes. Beware when I say minutes I mean minutes you gota work pretty fast.

I don't know how you will be able to remove air bubbles though. I normally use this method to make super cheap molds when that part in question isn't worth the cost of rebound or mold max.
 
The killer is saying $40 is too much. That pretty much eliminates any real molding/casting supplies, because a bag of plaster is $20, a couple pounds of alginate is $30, a trial size of pretty much anything Smooth-On sells is $30, 10lb of wax is $20, a quart of Bondo is $10, a quart of fiberglass resin is $20, and so on. To make a mold, and then casting, means you probably need at least 2 of these things. So that cuts out plaster, wax, aliginate, Rondo, ...



Even the silicone caulk is going to cost you like $8 a tube, and you'll need a couple. It's cheaper though, so it might get you closer.



Time to make a pepakura hand. haha :p
 
Yea. The box of alginate is about 12 bucks at hobby lobby and it looks like it will barely be enough. He is wanting to try and stay around $25. Its just the casting material im having trouble with. I was hoping that pouring in the brush on latex rubber would work but I wasnt sure.
 
I would try the wax. It's probably your cheapest bet. Maybe melt some in a cup and brush it on your hand in layers. Dip your hand in cold water, and remove drips, between layers. Then, with help of a friend, carefully wiggle out. Then you can slush in a layer of latex, let it dry, and repeat. I'm not sure what you could put inside the latex "glove" to fill it, though.



It's going to take a ton of time, but it will be as cheap as you can get. Good luck, and let us know how it goes.
 
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