Step 19: How Much Do I Need?

Quick disclaimer: The following numbers are what I experienced with my particular use of these compounds. Packing, humidity, the fact that not all the alginate mixed with the water, and my method of mixing allowed quite a bit of air to be entrapped are all factors that prevent the following information from being exact and precise. Please use it as a general guideline, and weigh your materials if at all possible.

This is the information I couldn't find when I started the project, and had to guess at, measure, and ask about before embarking on this project. These materials are sold by weight, and I could only find oblique references to possible volume. I ended up calling the company I planned on purchasing from for tips, and they suggested that 5 pounds of alginate and 10 pounds of hydrostone would be more than adequate to give me at least 5 small hand molds, and 12 or more castings. I purchased according to their recommendation, and you can see that the volume of the plaster powder in a 1 gallon tub is significantly less than the volume of the molding compound in a 2 gallon tub. I'll re-summarize my findings here:


Mix 3 parts water to one part alginate by weight. For loosely packed material this is 1 part water to 1 part alginate to get 1.5 parts molding compound by volume, including some air entrapped in the compound. This means that for each cup of mixed molding compound you need 2/3 cup of alginate, which corresponds to about 3oz of alginate. A 5 pound tub of alginate will make somewhere in the vicinity of 48 cups of molding compound, or 3 gallons. Note that the mixture volume is greater than the volume of the powder - 1 part of powder properly mixed with the water yields 1.5 parts of molding compound.

The bottom line here is that 3 ounces (weight) of this alginate makes about one cup of molding material once mixed. So if you need four cups to make your mold, you should purchase at least 3/4 pound (12 ounces) of alginate powder.

Hydrostone Plaster

Mix 1 part water to 3 parts hydrostone by weight. For loosely packed material this is 1 part water to 3 parts hydrostone to get 2.5 parts casting compound by volume. This means that if you need 1 cup of mixed casting compound, you'll need 1.2 cups of hydrostone powder, or about 9oz of hydrostone powder. The ten pounds of hydrostone that I purchased makes close to 15 cups of casting compound, which is just under a gallon. The volume decreases when water is added - 1 cup of hydrostone, mixed properly, yields .83 cups of casting compound.

The bottom line here is that 9 ounces (weight) of this alginate makes about one cup of mixed casting material.

How much I used

I tended to make more than needed, as I would rather waste a little now for a lower chance of making a mistake than mix less now for a higher chance of having to do it over again wasting even more time and material. Now that I've done it once, though, I expect I'll be more frugal in the future.

For the 6 molds I made (re-did the eldest's mold due to missing fingers in the casting, and did the neighbor's child when he visited as payment to keep the secret) the most alginate I used was 15oz, which made over 5 cups.

The smallest amount of alginate I used was 10oz, which made just over 3 cups of molding compound. In total the six molds took about 4.5 pounds of alginate.

Each time I made more hydrostone than needed - each hand needed less than a cup. I used nearly 5 pounds of hydrostone on two pours, one for 4 hands, and one for 2 hands. In both cases I ended up with enough extra to make several sand castings.


I spent about $85 after shipping for the materials. I have twice as much plaster as I need, and enough molding compound for another hand or two. Assuming I simply throw them away, each hand cost me about $14. I would consider this an upper-limit for the expense.
However, to save money, next time I would plan more carefully and do the following for each hand:
Find/prepare molding containers that suit the hand volume better.
Use about 8oz (5 cups mixed) alginate, which costs about $5
Use about 10oz (Just under one cup mixed) hydrostone, costing about $1

So the lower limit for a child's hand would be $6 each, not including shipping of materials. In the future I expect that I'll probably still use more than needed, and will simply round each hand to costing about $10, which is half what carnival and art fair hand casting booths seem to charge in this area.
<p>Two Day Classes Available at: <a href="http://www.lifecastingschoolofart.com" rel="nofollow"> www.lifecastingschoolofart.com </a> </p><p>Make it your home business and enjoy the process.</p><p>Life</p>
<p>Does anyone know how to repair /seal a hole or rip in an alginate mould prior to casting from it? Thanks, Sarah</p>
I hav dne a hand casting i got an isuue with the alginate.I got so many lumps in my alginate mixture i waz mixing it hard but the small alginate became so hard soo what should i do ..nd did no use ny blending machine 2 mix...nd my cast was kinda ohk..nd this was my 1st cast
<p>These are GREAT instructions! I did this with my husband, as a test run, and then with my granddaughter several months ago, and it went really well. The detail is fascinating. I'd like to be able to make replica's of my granddaughter's cast for family members, as she's grown some now, and isn't as cooperative, even when asleep. Have you tried making an alginate mold of the hydrostone, or do you think it would stick? If I used a release agent, would it stain the original? Her fingers were slightly curled, so I'm a little bit afraid of breaking the original. I wish now that I had done several at that time. Any suggestions or recommendations?</p>
<p>I'm planning of doing a cast of my own hand as a jewellery holder, and was wondering if you (or anyone) knows a good paint and gloss to use so I can paint it black and then add a transparent top coat?</p>
<p>Make sure the plaster is <strong>completely </strong>dry before you try painting it. Give it a week or two. If it feels cold it's probably not dry yet. After that, any type of brush or spray paint should be fine. Try Krylon. They make a clear coat also.</p>
<p>did u get a reply yet?</p>
Hiii i want know do you teach that in class so college because i'm to interested for it i know how to make it but the problem is when become a solid i don't know how to fix it properly so do you know or have any college please,thanks
Okay, so I know how to actually make the mold, insert and remove hand (or whatever), but can somebody please tell me exactly what the products I need are called? I need the moulding agent, and also the plaster that forms the actual cast. Can somebody please tell me as simple as possible; what its called and where I can buy it? (Prefer a very strong &quot;stone like&quot; plater, or a harder material of some sort)<br><br>(Sorry if this has already been asked,but I have tried looking all this up myself and it turns out that I'm hopeless with the internet and I have no idea what to search for as I don't know the name of the materials. I'm surprised I even made my way to this page! XD )
I detail the exact products I used in step one - requirements and preparation. Here are the two products:<br><br>For the molding compound I used ALG-390 from Special Effect Supply Corporation, which is a 3 minute set alginate. You can find other suppliers, just search for &quot;3 minute alginate&quot;. The ALG-390 I used can be found here, halfway down the page: http://www.fxsupply.com/life_casting/casting.html<br><br>For the plaster I used a particular formula called Hydrostone which features high strength, and high detail. This also came from FX Supply, as item HYD, and is a 20 minute set plaster. The HYD I used can be found here: http://www.fxsupply.com/materials/plaster.html<br><br>There are a variety of other molding and plaster compound you could use - I understand a lot of people used plastic and epoxy products from Smooth On rather than plaster for very durable parts.<br><br>There are many, many sources for all parts of this process. If you still feel unsure, do an internet search for &quot;lifecasting supplies&quot; and you'll find a great deal more information and products you can use.<br><br>Good luck!
Thankyou so much!! :)
Very cool, here is my experiment pic! The bigger is mine, the medium is from my 4 years son and the smaller is from my 2 years son.
<p>Hello Cartola!</p><p>What material have you used to make the cast?</p><p>I have used dental plaster but the gold paint either does not stay (spray paint) or the regular oil paint is too thick and covers recorded details. Could you please advise. </p>
Oh, and I've never tried to paint them :)
Hi! Those were my first tests I guess. In the first ones I've tried with that industrial silicon that comes in tubes, for general home usage. The best one at the end was the alginate, used by dentists. The &quot;problem&quot; is that you can use them only in the same day, so, if you want to make many units it wont be possible. The final and best solution I've used was with alginate for the mold and liquid silicon for the pieces.
I have made a couple using latex gloves filled with plaster. I had a problem with the fingers just snapping off. I let the plaster set for several days before removing the latex glove but it didn't seem to matter. I'm kind of stumped now cause I would still like to make thek. I thought about inserting wire down into the fingers but haven't tried it yet. I had planned on mounting them on small wood plaques or just setting them on a table, after I cleaned them up of course. If you use a latex glove it obviously wouldn't be a replica of a real hand.
<p>If you mix white glue into the plaster mix it comes out more compact. make the water quantity half glue, half water.</p>
<p>Perhaps the plaster you chose isn't suitable for objects such as long thin fingers. A wire armateure may work, but you might instead want to research better plaster or molding compounds that are stronger for the type of object you are making.</p>
<p>This is one of the most well written ibles I've seen, kudos.</p><p>Will be trying this at some point. For some reason I want an ashtray in the shape of my hand.</p>
<p>i had my deceased sons hand put on plaster and don't know where to go from that,,plzz help</p>
OK, I wanna try that now, would be kinda fun to stick my hand in alginate, actually.
Brilliant! Just brilliant. Well done.
This is just one awesome instructable I came across. A great write. Thank you for sharing.
Once you have made the alginate mold, you can pre-cut it in half BEFORE you pour the casting solution. You would then put it back in the carton you made it in, if you cut it off carefully, and use wire, or other binding device, to make the whole thing tight. There may be a slight line from the mold being cut apart, but, with practice, you could probably minimize this, perhaps cut the mold in half at an angle rather than straight into it, would minimize the line. This would also be a great time to add a small air vent to any area that may need it, in the alginate mold. I have seen this done before using a fat stick and other items to make candles, using wax as the casting.
would this be strong enough to hold a guitar on the wall?
You'll need to check out the properties of the compound you use for the final object. I suspect hydro stone would be, it's rated to 2,000 psi or so, but it can be broken with very sharp blows. You can also reinforce yours with wires internally before pouring the compound into the mold.
Beautiful, a great idea!
Will this technique work for a mould of a clenched fist? I'm not sure if I'll be able to get my hand out
Yes. In fact on step 16 you'll see there are two clenched fists that I pulled, and two open hands.<br><br>The alginate is very flexible, and will stretch and move quite a bit without tearing. An adult clenched fist will be able to come out quite easily.
Thanks, I might do this for a fundraiser at school
Very helpful Instructable; I just tried it myself and it's almost creepy to see your own lifeless hand... Thank you for the inspiration.
I've done this project one afternoon in art school with alginate and plaster of Paris. It turned out beautifully and was a great experience. Since then, I've seen in a craft show a man who sold moldings of hands placed so they could hold a business card, a toothbrush, etc... There even was a, ahum, male body part made for stacking bracelets (my grandma was a bit shocked upon seeing this!) Quite entertaining.<br>Thanks for the detailed instructions, I had forgot a few details. Maybe I'll try to make a business card holder with my hand!
Try flexwax to make the mold. It melts at a low temp, gets lots of detail and can be used over and over.
Wow, I´ve made more with liquid silicon. Much better than plaster. Children can play with them without beeing afraid of breaking. And you can also try to use the same mold to do more than one copy, as the silicon is flexible and the hand gets out of the mold without breaking it.
COOL!!! I want to make a mold that you can use it many times without break it!!!! can i create a plaster hand and then use it to create the mold with liquid silicon? Well hope that works!!!! If someone know Please tell me how to do it, or if my idea can work then thumbs up for me jajaj!!!
Hi. In my experiments I noticed that the liquid silicon will get glued to the plaster. I think maybe some oil can keep them separated. Probably the best way to do a reusable silicon mold is make it in parts, otherwise I guess you won't be able to get the plaster hand from the mold without breaking it. There are some instructables around here that shows some ways to do two part molds. The alginate mold can be used some times, but it is not a very resistant material and even if you don't break it it will probably not be usable for more than a week. To try to make it last more time, keep it involved with a humid towel. Good luck!
For some reason that hand looks kinfa freaky like that.....
You can never be too sure about those pesky toddler zombies. They scream "NO!" as they climb on the table and attempt to eat your brains. Unless Yo Gabba Gabba is on. Then they behave.
Alginate is actually the best compound to use for molds with children as models. I had my hands and arms cast in plaster - at art college - and trust me, it hurts. It hurt enough for an adult to be very uncomfortable, so with children it would be even more difficult. Alginate does not warm up a lot and does not expand, the expansion of the molding material causes joint pains, from the pressure and it heats up enough to be close to painful. Alginate is also more gentle on the skin. To make a mold for more copies, it might be better to plan better the poses, and to do the mold in two or more parts, not just cut up a mold. Then you can see trouble before it happens. Since alginate is slightly pliabe, it's more forgiving than plaster. I molds of both my arms above the elbow made, and we copied them in resin - the same stuff used to make surfboards - with some marble powder mixed in. It was a lengthy process, over an hour for each mold - making barriers, to make sure I could remove my hand without breaking the mold and after curing the resin we did have to break the mold. One copy took maybe five hours for a team of three adults to make. Lots of work.
To ensure fine detail in the plaster pouring stage make a thinned out plaster slip. Pour a small amount in the mold and rotate. Remove excess and repeat 2 to 3 times, then do your final fill. You can also hollow at this point by filling a balloon to take up space or some other filler. Be sure to coat with petroleum jelly or silicone spray to remove.
Air, is your enemy in both alginate and the 2 plaster stages. Alginate + plaster - you can't help put air in to, as you need to mix them both with water to start the chemical reaction. Both alginate and plaster, you can bang in containers, to try to get the bubbles to rise (mind splashes) but one thing you can do to help your final cast immensely, is to fill the alginate mold with water, then tip the water out, gently swill a small amount of plaster around the mold, turning it upside down and everything, then carefully pour more plaster inside your mold, always tapping the mold on a surface. Don't just pour plaster in, and think it will be ok- air is the mold makers arch enemy!!! You can experiment with making a one peice mold, and cutting it down the middle, fill both sides then stick em together- although I reckon you'll get flash lines. And the correct term for "Overhangs" is Undercut :) Happy molding - make a candle :D
Oh! I forgot to say- the air bubbles, before you put the hand in the alginate, paint the awaiting mixed alginate on to the hand, THEN put it in the mix, this helps make a skin of alginate which will join the rest of the aliginate in the tub. It's not always 100% but it helps.
You have seen those life size plaster paris decorative hands that are made for a way of hanging your jewelry? You could make one of your own hand and give it to a friend as a gift.
I was just thinking, I'm going to make one of this, and get a small threaded rod, and stick my semi-open cast into my wall! And I shall hang my keys, or hat from it. Stellar instructable!
I do these, but I cast the hands in acrylic resin instead of plaster - you can get pretty much any color, and if you feel creative you can use plain clear resin and toss in glitter, sprinkles, anything interesting...
You cast the hands in acrylic resin? Do you use the same molding material? I was wondering if the wetness of the mold messes with the resin. I cast hands and would love to do some in acrylic. Also, how do you fix all the imperfections? Some of my hands <a rel="nofollow" href="http://www.photobucket.com/marylouart">http://www.photobucket.com/marylouart</a><br/>
Yeah, I've used plain old dental alginate as the mold material, and then the 2 part resin mix from the craft store. I've only ever done baby hands, but an adult hand would be pretty much the same (it would just take a LOT longer to dry). The way I do it is to stick the hand in the mold, wait for it to set, remove the hand, and then I let the mold sit for another minute or so. Pour the liquid acrylic in, and very gently tap the bottom of the mold against the table (although if you have access to an agitator, they work really well - my father in law owns a dental lab, so I can use his agitators whenever I want. They aren't really necessary, though). Surprisingly there aren't too many imperfections, mostly because babies pretty much only have closed fists. For adult hands, if you don't mind a frosted look, you can use a dremel with a felt bit to smooth the whole hand. If you don't mind extra work, you can also hand buff the acrylic with those 4 sided nail buffing bars. It doesn't get it as shiny as newly poured acrylic, but it looks good with colored acrylics.
Thanks rhondalicious, great info.
wow, very good, so much detail and techniques described and a fantastic outcome, a very original present :D

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