Casting Using Dental Stone
|In my opinion, these are the absolute best casting materials to use. The plasters listed here are actually not "plasters" at all but are known as Die Stone or a Dental Stone. Other brand names can sound something like Die-keen or Veri-die or Apex Stone. Usually if it has Die or Stone in the name, it's probably much harder than your regular plaster.|
There are several kinds of dental stone so whatever you buy, always look at the compression strength measured in psi (pounds per square inch).
- Regular plaster of paris is 5,000 psi compression strength and will chip fairly easily.
- Hydrocal is around 8,000 psi and is more durable.
- Merlin's Magic (reviewed below) is around 14,000 psi and is even more durable yet.
- Excalibur and Die-Keen (also reviewed below) are 18,000 psi and dry so hard it's almost like a ceramic material.
Merlin's Magic is made by a company called Garreco. You can purchase it from several places. Most of these companies drop ship from Garreco (send the order to Garreco who ships it directly to you) which means that all their dental stone is sent from Arkansas using UPS Ground. Shipping may be fairly expensive depending on how far you live from Arkansas.
- Swords of Honor (located in Idaho). They have an online shopping cart and offer several colors of Merlin's in 5 lb, 10 lb, 25 lb and 50 lb packaging. They also sell lots of cool swords and historical gear.
- Atlantic Dental Supply (material is shipped from Arkansas). They accept Visa and Mastercard and have an online shopping cart. You can call them at (919) 321-0938 -ask for Bethany.
- Merlin's Magic Plaster (located in Indiana). They ship smaller quantities such as 5, 10, 15 and 20 pounds of all colors available and can drop ship 25 and 50 pound boxes. They only accept Paypal and have an online shopping cart. You can call them at (774) 277-9619.
- Canyon State Dental Supply (located in Arizona). Their phone number is 1-800-354-3684 - ask for Steve.
They accept Visa, Mastercard and American Express. They don't have an online shopping cart but you can place an order over the phone.
- Clint Sales (located in Massachusetts). They don't accept credit cards or have an online shopping cart but they do take Paypal. To order, call Cindy at (978) 927-3010 or send her an e-mail at email@example.com. If you are in her region of the US she can save you money on shipping.
Merlin's Magic comes in white, tan, gray and dark gray. Personally, I would avoid the dark gray. Maybe it's just me but I've found that the dark gray has so much non-soluable pigment in it that tiny micro-bubbles form, kind of like foam that won't go away. I found that the tan or white colors take stain very well for the wooden plank and wood shingle pieces.
Mixing Merlin's Magic
Merlin's Magic is a special kind of casting material. It's made to pour into molds easily with very few air bubbles. Because of this special ability, I found that I needed to mix it differently than regular plaster. Below are instructions to mix up enough plaster to fill one regular size mold.
First you need to make a measuring cup that can be reused.
- Get two disposable plastic cups and nest one inside the other.
- Pour 2 ounces (60 ml) of water into the top cup and place a black mark on the outside of the bottom cup where the water line is.
- Place an additional 2.5 ounces of water into the cup (for a total of 4.5 ounces or 135 ml). Then place another black mark on the outer cup at the water line.
- Remove the inner cup and you have a reusable measuring cup.
Here is how you mix the plaster
- Insert a new cup into your measuring cup.
- Pour in water until it reaches the first line.
- Carefully shake in the powder until the mixture reaches the second line. The powder must be absorbed into the water before you can determine if the second line is reached.
- Remove the inner cup, mix up the plaster and pour it into your mold.
If you would prefer to mix the stone by weight instead, here is a table that may help you. However, you will need a scale to measure the weight of the powder. Please note that the "ounces" shown here are a liquid measurement (not weight).
molds to fill
|Ounces (or ml)
|Amount of powder|
||2 ounces (60ml)
||4 ounces (120ml)
||6 ounces (180ml)
||8 ounces (240ml)
Also, the mixing instructions on the package of Merlin's Magic will be different. Their instructions are used for dental castings, which use a vibrator to shake thicker plaster into their dental molds. If you mix according to their instructions, the plaster may be too thick to pour into a mold.
Overall I believe this is the best material for beginners to use.
- It's very strong, but you can still carve or sand it without too much problem.
- It mixes and pours very thin, much thinner than any other casting plaster I've used. Because of this, it also reduces bubbles better than any other plaster I've used.
- It scrapes much cleaner and has less sinkage than Excalibur (that's when the particles of plaster sink down into the water leaving your blocks short). Because of this, bottom of your scraped blocks will be more exact.
- It cures faster than most plasters (around 15 minutes). Most plasters take around 25 minutes to set up.
- It takes paint and glue better than plaster.
- It's slightly heavier than regular plaster. Plaster blocks weighing 1 pound would weigh 1 1/4 pounds using this material.
- It's not as strong as Excalibur, but I doubt anyone could tell the difference.
- It's a little more difficult to mix it by eye (but I still mix it by eye myself).
- It's more expensive than other plasters.
Excalibur and Die-Keen
Excalibur is also made by a company called Garraco and can be purchased from the companies listed at the top of this web page. Die-Keen is manufactured by a company called Heraeus Kulzer.
These two products are almost identical, only the makers of Excalibur have made their product come in the colors of white, tan, gray and dark gray! It doesn't matter which color you pick, they all have the same properties. I found that the tan or white colors take stain very well for the wooden plank and wood shingle pieces.
||You mix this material just like you mix plaster. The Excalibur I'm using is light gray in color (and fairly heavy). Start with a 1/3 cup of water and gently shake (sift) the powder into the water. It will sink quickly.|
Continue to add the powder until the water won't soak up any more. If all of the powder is wet and there's no layer of water on top, then you've mixed it perfectly.
|Gently stir the mixture to remove any lumps. I swear, dentists have the best stuff. The material mixes smoother than any type of plaster I've ever worked with.
||Spoon the mixture into each pocket of the mold. Sometimes it helps to pour the blocks 1/2 way, tap the mold sharply to remove air bubbles (I use the handle of my putty knife), then fill them the rest of the way.|
Even mixed at full strength, this material is thinner than plaster and will flow into the corners easier. Be sure to overfill each pocket.
|Let the stuff set in the mold for about 3-6 minutes. Take a putty knife and poke at the edge. If the edge is the consistency of toothpaste, then go onto the next step.
This material doesn't act like plaster! As the mixture sets, wet particles continue to sink down into the mold, leaving a layer of water on top. The edges around the blocks will start to set up but the middle of the blocks will still be very liquid.
|Lay a paper towel over the mold and let it soak up the excess water that rises to the top.
This is why you want to overfill the pockets slightly. If you don't, when you soak it up the excess water your blocks will be short.
||Gently scrape across the mold to remove the excess. The mixture will be thin, so you may have to scrape back and forth a few times to level it.|
The excess won't come off neatly. Let it run off the side of the mold onto your work surface. Once it hardens it will pop right off the work surface easily. Let it set 25-30 minutes before you remove the blocks.
|The dental plaster is really strong! I threw a stair section on the floor as hard as I could and it didn't even chip! It also takes glue and paint really well.|
Here's a comparison of the advantages and disadvantages of Excalibur and Die Keen. Overall I was really pleased with the results and will be using these for most of my casting.
- It's incredibly strong. I haven't seen a material as strong as this (except in plastic). The downside is that it's harder to sand and carve.
- It mixes thinner than most plaster (but not as thin as Merlin's). This gives you fewer air bubbles than you would have if you used regular plaster.
- It cures as quickly as plaster (about 25 minutes). A lot of hydrocal and hydrostone mixtures take longer.
- It takes paint and glue better than plaster.
- It's heavy. Plaster blocks weighing 1 pound would weigh 1 1/2 pounds using this material.
- Excalibur sinks down in the mold. As the plaster particles settle, you'll get a layer of water on top of the plaster. If you scrape the mold too soon, your blocks will end up being short.
- It's more expensive than other plasters.
http://www.hirstarts.com. All photos, articles and plans are copyrighted by Bruce Hirst and may not be used without permission.
"Castlemolds(R)" is a trademark of Hirst Arts Fantasy Architecture Inc.
For more information contact firstname.lastname@example.org.