After a few minutes, they would wriggle their hands free, and the operator of the booth would pour a plaster compound into the mold, and have the customer return in 30 minutes for the finished piece.
My coworker didn't pay to have his hand cast, but instead did a little research online, and for Christmas obtained all the materials and did casts for all his nieces and nephews.
Since that time I've wanted to do it for my children, but for various reasons never did so. I decided I would try this out for mother's day - if I make four molds, one for each child, then make three castings from each mold I would have enough for a complete set of four for their mother and each grandmother.
This is a Mother's day present I can really sink my hands into!
Step 1: Requirements and Preparation
AlginateThis molding compound forms a rubbery elastomer within minutes of mixing with water. Captures impressive detail, while being flexible enough to prevent entrapment of the hand. It dries and shrinks over time, so it's not suitable for more than a few castings. I used ALG-390 from Special Effect Supply Corporation, which is a 3 minute set alginate.
Casting PlasterMany plasters are available for casting, you can even use the inexpensive local plaster you find in any hardware store. 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.
Mold containersI used 1/2 gallon jugs, 1/2 gallon juice bottles, and 2 liter pop bottles. The only difference was that when I needed to cut away the mold, the plastic juice bottle and 2 liter bottles were a little harder to cut.
Hot waterA cold mold is uncomfortable, so start with hot water. By the time you get it mixed it should be at a comfortably warm temperature.
Machine screws and nutsIf you don't want to break the mold, you have to have something sticking out of the casting once it's hardened in order to pull it out. Can also be used to mount the finished piece onto another project.
Small pieces of cardboardUsed to hold the screws in place while the casting cures.
MixerI used a cordless drill and one egg beater. A regular mixer should work, and for large batches a jiffy mixer (paint mixing drill attachment) is recommended. Don't plan on mixing this by hand as there isn't enough time. Also note that the plaster is abrasive and may damage the beater.
ScaleThese materials settle and compress so they should be mixed by weight. However, the working range of the mixture is pretty good, and in a crunch I believe suitable result can be obtained from volume measurements which will be detailed below. I'm using a postal scale that can measure in tenths of ounces up to 10 pounds, which is the range needed for small hand molds and casts.
Containers & cupsYou'll want to stage your materials, measuring both the water and powder into separate containers, and then mix them together. Therefore you'll need containers suitable for holding the pre-measured materials. The cups are useful for scooping powder out of the supply buckets.
Watch or TimerYou'll need to time the molding process fairly carefully to obtain good results, so keep a timer handy. When you're elbow deep in any project it can be hard to accurately judge time.
Box knifeUsed to cut the molding container top off, and later cut the container away from the mold when you want to break the mold.
Long sharp knifeI found it necessary to cut and level the top of the mold so the cardboard holding the screws was level. A knife long enough to cut all the way through prevents tearing the mold.
ScissorsUsed to cut the top off the molding container, and is more convenient than the box cutter for some containers once the cut is started.
Pocket multi-toolUsed for a variety of tasks, depending on your skill and the tool it may replace several of the other tools.
Plastic forks, paper towelsNot necessary, but you may want them on hand for various tasks, such as scraping hardened molding and casting materials off various surfaces, cleaning spills, etc.
Please note that while the materials are not generally toxic (check with your supplier), you should not use any of these tools for food later.
Tool/Material layoutYou'll need a full table for your first time. It can be done in a smaller space, but room to work is helpful as you may be worried about time during the molding stage, and looking for a spot to set the water pitcher is a distraction.
A chair for the person whose hand is being molded is nice. People tend to shift their weight frequently when standing, which can cause a mold to be damaged while setting.
A utility sink is useful for later cleanup.
Assistants: This can be done alone, though in my case I had four eager assistants helping me by taking pictures, holding containers during mixing, and providing opportunities to practice my collision avoidance and balance during the process.
Step 2: Caution/Warning
Also follow general project safety rules. Handle knifes and other sharp objects with care - prepare so you don't have to use them in the presence of children, animals, and skittish spouses that have seen you work before. Wear safety goggles when appropriate.
Step 3: Glossary - Definition of terms
AlginateA material found in algae, seaweed, and some bacteria. Most alginates used for molding are made from seaweed. When mixed with water they cross-link (similar to plastic) and trap the water into a moist, rubbery material. Over time the water evaporates and the material shrinks, hardens, and deforms.
CastingUsed as both a verb and noun. Casting, verb, describes the process of making a casting from a mold. Casting, noun, refers to the part pulled from the mold once the casting compound has cured. The part pulled from the mold is generally a "positive" part, exactly duplicating the original part molded.
HydrostoneA form of gypsum plaster, when mixed with water cures into a long-lasting, hard material without shrinking. This is slow setting, and pours well.
ModelThe person and/or object being molded.
MoldThe form for the casting, formed as a "negative" out of a molding compound which cured around the original.
Setting/curingUsed interchangeably in this instructable to describe the process a molding or casting compound goes through to harden.
Step 4: Process summary
1. Measure water and Alginate for mold
2. Mix water and alginate in molding container for no more than 45 to 60 seconds
3. Place object to the molded into alginate mixture
4. Hold object still for 3-5 minutes
5. Gently wiggle object free from mold
6. Measure water and plaster for casting
7. Mix water and plaster
8. Pour mixture into mold
9. Place bolt or other fastener into casting
10. When cured (20-30 minutes) remove casting from mold
11. Allow casting to cure for additional 24 hours before working on it or painting it.
Step 5: Prepare for mold
I did not instruct my children to wash their hands before molding. The natural oils act as an ok mold release compound, although clean hands should make a better impression of fingerprints and tiny features. They should certainly be instructed to wash their hands afterwards.
Step 6: Measure molding compound and water
You'll see later that due to the containers I chose, some molding powder never mixed with water, so I often ended up with a mixture that was low on powder. It worked fine, so there is some working room.
Measure the powder in the molding container, and the water into a separate container, and plan on adding water to the powder, rather than powder to the water. My first attempt I added the powder to the water, and it didn't mix into the water as quickly as I needed - a lot of powder ended up on the table.
Use warm or hot water to make the model more comfortable. 90F to 100F (32C to 37C) was suitable. Having warm water is especially important for sleeping babies.
Step 7: Mix molding compound
Try to keep the beaters below the surface of the water to avoid adding more air to the mixture as this will result in bubbles in your mold.
Also do not beat the mixture for more than 45 seconds or so. Remember that this is a 3 minute cure molding compound. If you mix for too long you'll end up with a bad mold. Don't worry if the mixture still looks lumpy and not completely mixed.
If you have a vacuum chamber you can remove some of the bubbles from the molding compound by pulling a light vacuum from it. It may foam up, so be prepared with a large container, or a willingness to clean up a mess.
Alternately, firmly rapping the container against the table should bring up many bubbles as well.
Step 8: Place model in molding compound, wait for cure
I earlier instructed the model to place their hand into the molding compound in an open position, then move and wiggle for several seconds before settling into the final position. This helps adhere the alginate to the hand, preventing bubbles from settling near the skin and in the crevices between fingers.
While the hands were in the mold I held the wrist firmly. This serves two functions:
1. You can help them hold the hand steady to prevent large movements from tearing the mold before it cures
2. You can feel the tendons in their wrist move as they work their fingers. This will help you know when to remind them not to wiggle, as children will often work the unfamiliar, squishy, warm material in their hands if not monitored.
Babies are especially prone to hand movement, so often it is best to do this while they sleep. Make sure the molding compound is warm to the touch, but not hot, and make sure the baby is in a comfortable position for the mold. As you can see in the picture, our youngest child woke up during the process, but was still laying comfortably and only required a little singing to prevent wiggling and worrying. As you can't easily instruct the baby to wiggle their fingers or move their hand in the beginning you'll have to move it around by the wrist when you insert the hand. In this case I pushed the hand in, moved it side to side to side to side, then partially removed and re-inserted it.
I usually wait about 5 minutes from the beginning of mixing until I attempt to pull the model from the mold.
Short hair is not typically a problem, it pulls easily from the mold, but if the model has long hair or thick hair on the part to be molded you may consider using a mold release compound to prevent discomfort and mold tearing, such as a little petroleum jelly. Children and most adult hands won't have this issue, but keep it in mind. Also note that rings are duplicated, but some rings will tear the mold during removal. You might try having the child hold an object (ball, toy block) or molding with a ring, but leaving the ring in the mold. These objects may either be removed from the mold and be replicated by the casting compound, or you may leave them in the mold to become part of the casting, as rings and balls can be difficult to put into place on a hardened casting.
Step 9: Remove model from mold
The mold is flexible and will open as they remove their hand. Occasionally pushing the wrist and then the hand away from one or the other side of the mold will allow air to enter the mold, which will make it easier to remove the hand.
Rub excess molding compound from the arms and hands of the model. While they are small and non toxic, pieces of molding compound still pose a danger to small air passages.
Step 10: Prepare for casting
Note if the mold has any overhangs that will form air pockets when the casting compound is poured.
Prepare the fasteners to be held in place during curing. In my case I chose to embed the nut into the casting, so I attached a screw and pushed it through a piece of cardboard which would rest on the mold during curing. If you insert a dowel into the casting you will be able to use wood screws to attach the casting, or chip the wood out later and use epoxy in the hole left behind.
Step 11: Measure and mix casting compound
For those who wish to measure by volume, I found that loose Hydrostone powder can be mixed as a 1:3 water:powder by volume, and would result in about a 2.5 volume mixture. So 1 cup of water (about 9oz) mixes with 3 cups (about 27oz) of Hydrostone to make about 2.5 cups of plaster mixture.
Do not use hot water. The compound is exothermic and releases heat as it cures. Further, the compound cures faster with warmer water.
As there is no significant time factor here, you can take your time mixing the water and casting compound together. Note that the resulting volume is more than the water volume but less than the casting compound. For this reason I also mixed the water into the powder.
Try to avoid letting air mix into the compound, but mix it thoroughly.
If you let it sit for more than a minute after mixing, consider mixing it again before pouring as it will settle and result in a thinner mixture being poured.
My 7 year old's hand has a volume near 2/3 of a cup, so for four hands this size and smaller, 2.5 to 3 cups should be sufficient.
Step 12: Pour casts
While twisting the mold around, pour the compound back into the casting mixture. By pouring it out, small bubbles that form against the mold are popped, and a thin layer of casting compound adheres to the mold. This will also help you find air pockets in the mold that may require extra attention by observing how the liquid pours.
If the mold has overhangs, they may form air pockets that will prevent the mold from completely filling. You have to pour a small amount of casting compound into the mold, and then tilt it so the air bubbles out from under the overhang and traps casting compound under it, then add more and repeat the tilting until full. This is not fool-proof. If you anticipate an overhang, you may consider adding a straw to the mold during the molding process, or before casting so the air can escape. This will add an easily detached rod to the casting.
If I had a vacuum chamber, I would pull a vacuum on it to reduce bubbles in the casting compound. Instead I picked up the filled mold, and struck it against the table several times to encourage bubbles to the surface.
Step 13: Place fasteners into compound, wait for cure
If you made too much plaster (!) you have time to mix another batch of molding compound and mold something else. I chose instead to wet down the sand box and make a few sand castings (faster and cheaper than an alginate mold). If you live in an area frequented by wild animals you can make castings of their footprints by placing a paper ring around the footprint, packing a little dirt just inside the ring to prevent leaks, and pouring the plaster inside the paper form.
Wait for plaster to cure. This will take at least 20 minutes, but I generally waited 30 or more minutes.
Maybe use the time to catch up on some important reading.
Step 14: Remove part or break mold
I knew by this time that I wouldn't be able to remove the hands without tearing the mold or damaging the hands. Further, the movement of the plaster inside the mold may damage some of the fine details of the casting, so I chose instead to make cuts in the mold and tear it apart in order to remove the casting.
If you don't mind damaging this casting, and you have a very good idea of where inside the mold the casting is you may be able to turn it into a two part reusable mold. Cut carefully along the edge of the mold until you reach the casting inside. Add a few irregular cuts so it will be easy to re-align the mold again during the next pour. The knife will cut the casting a little bit, and future castings will have a part line where the mold was cut. Make sure you can remove one side from the other without tearing, and pull the two halves of the mold apart. Remove the casting, and inspect and clean the mold for the next casting. You'll have to support the mold externally (another bottle, or perhaps strips of fabric or tape that won't cut into the mold). Keep in mind that the mold is going to dry and shrink significantly over the next 24 hours, so it won't last for long, and each casting will damage it a little more.
Step 15: Inspect parts - common problems
Air bubbles in the mold show up as bumps in the casting. This could have been reduced by mixing the molding compound carefully to avoid introducing more air, pulling a vacuum on the compound to bring bubbles to the surface (it will foam, so make sure you're prepared for a mess), and having the model move around so the compound adheres to the object, causing any bubbles to form away from the model, rather than next to it. I removed the larger of these from the casting simply by pinching them with a set of pliers. A file, sandpaper, or rotary tool with a burr would work as well though you lose detail the more material you remove. This is by far the most common issue, and one of the easiest to fix. Still, make sure they wriggle their fingers and move their hand around a lot before holding the pose during molding.
Air bubbles in the casting show up as voids and holes in the casting. This could be reduced using methods similar to those mentioned above for the molding compound. Also, as the compound is fairly liquid and takes some time to cure, a vibration table may also work well. These could be filled in with a variety of materials after the casting has cured.
Incomplete casting. If you expect a large air pocket due to an overhang, consider drilling or cutting a hole through the mold into the overhang to allow air to escape. I haven't done this myself and can't offer much advice, but I expect a sharpened metal tube could cut through the mold. Alternately, set tubes in the mold during the molding process. You may be able to fill the void by tilting and turning the mold during the casting process. There isn't much you can do here post process without a lot of work. Depending on the model you may instead remove more of the material so it appears as though it were suppose to look that way. If you still have the portion of the mold that didn't cast, you might try pouring a smaller section again and then carefully grafting it all together.
I've re-done the hand with missing fingers, but I'm leaving the rest of them alone for now - I want to preserve the detail that was captured, in spite of the flaws that were introduced.
Step 16: Hide the parts, avoid suspicion
Clean up, but don't clean up so well that questions are asked.
Step 17: Presently present presents
Carefully wrapping the castings, I then had each child present them to their mother, youngest to oldest, and then gave the poem last.
As I expected, and as the poem alludes to, my mother-in-law was much more impressed by the gift than my wife. When you can hold the hands each day you tend not to need reminders. Over time the gifts will become more precious.
It occurred to me later that the gift might have even more impact if given several years after it was made. Perhaps when the nest is empty, or when you have your first grandchild.
This is also a great interactive gift. Consider bringing enough materials to a family gathering, maybe this next fall holiday season, to do this for nieces, nephews, and new couples. It requires more material and coordination, but a mold can be made of a couple holding hands.
Step 18: Mount parts
Prepare the casting for mounting by sanding the mounting surface of the casting flat, and ideally parallel to the fastener. Scratch name and date of the casting into this surface where it will be hidden from view but accessible if needed later to resolve inevitable fights over who's hand it really is later.
There are many engraving companies that will engrave a simple metal plaque with the poem, child's name, and date online as well as near you. Look in the phone book for trophy places, or jewelry shops.
As there are many other opportunities and methods for mounting the finished work, I will leave this for another instructable to come. Some suggestions:
Clearcoat the casting with paint or epoxy and use it as a paperweight.
Mount it to a board, then hang the board on the wall using the castings as coat hooks.
Make a mobile out of them - make certain they are secure, each hand weighs over a pound and will hurt if they fall on you.
Have the children form sign language words and letters, then mount them in series to a longer board.
Plan ahead to do this each year or two, and make a mount that shows growth over time, including pictures in front of a height measure of some sort.
Keep in mind that while the parts are made of fairly tough plaster, it is still easy to scratch and damage. Clearcoating, or painting, is recommended for long term durability. As the part is heavy and cold (high thermal mass), a bronze or other metallic paint will cause many to wonder if it is really metal.
Make sure the part is carefully secured to the mounting board. Any looseness in the mounting will, over time, cause the fastener to work loose from the plaster. Compatible epoxy will also hold an unfastened casting to most materials.
Step 19: How much do I need?
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:
AlginateMix 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 PlasterMix 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 usedI 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.
CostI 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.
Step 20: What went right, what went wrong, what I will do differently next time
As you can see, I had two fists, one open hand, and one slightly closed hand. Most who saw these indicated that the semi-closed hand was the favorite, partially for the reason that an adult finger would fit inside just right, and the fingers could be felt separately.
I did not fully meet my goal. I wanted to pull several hands from each mold, but did not carefully consider the problem of overhangs, and the fact that the fist and hand are larger than the wrist. With suitable mold release compound one might still succeed to some limited extent, but I expect a 2 part mold would work better, and I will attempt that in the future.
The project was a lot of fun, and very satisfying. I expect I'll be using these methods to mold other objects in the future, and trying out other casting compounds such as latex and epoxy. I fully expect to do something similar for creating parts of my Halloween costume, and perhaps decorations, in the fall. The hydrostone would make excellent shards of skull or bone, and latex works great for hands, fingers, and masks.