Introduction: Slip Cast Ceramic Trophies
So here is the skinny. Each year at our school we have an end of the year awards ceremony that recognizes students in academics, sports, and clubs. During this ceremony I have a handful of art students who earn awards in various mediums. About a week before this years awards were to be presented I decided when needed to up our trophy game and we decided to slip cast our own art room trophies.
In the following Instructable I will explain the ceramic slip casting process and how you could use it to make your own custom awards... or anything really.
Disclaimer- This Instructable contains photos from many different projects to help illustrate each step of the process.
Step 1: Brainstorming
The whole process started with an idea. Earlier in the year we dabbled with slip casting as a class and through trial and error found a process that worked very well for us. Once we decided to use a slip cast idea for our trophies we needed a design to work from.
We wanted our awards to have a classic look like and "Oscar" or "Golden Globe" but with an art room flare. We eventually settled on this strange plastic cup I had in my collection of random classroom decor.
Step 2: Coddle Boards
After choosing the model we need to find a little bit of info about our casting.
1.How many parts were going to be needed for this mold?
This is a pretty complex mold but not complex enough to warrant more than 2 parts. As long as a design doesn't have any undercuts, so the plaster can release freely, you can get away with a 2 part plaster mold.
2. How large the coddle boards would be?
Wait, wait, wait... whats a coddle board? Coddled boards are the white "L" shaped walls you see us building around our design and pouring plaster into. The are very easy to make and because of their "L" shape and with the help of a few clamps they are adjustable for different designs. You want about 4-5 inches of plaster on either side of a design to help with the drying process. These coddle boards needed to be tall enough to hold all the plaster as well, so I have included a picture of shorter coddle boards as well.
3. How much plaster to mix.
This is where math comes in. We need to know the overall volume (Height X Width X Depth = Volume) needed to fill the space with plaster. after you find your total volume you need to cut it in HALF before mixing plaster since you are only doing one half at a time.
Step 3: Supplies
To make a plaster cast for slip casting you will need both Plaster and Slip... shocking I know.
I use a standard pottery plaster that sets up in about 1-2 hours and does a really good job holding onto details. Buy more plaster than you think you will need cause it takes a lot to make sizable casts.
You will also need liquid slip. Slip is NOT just watered down clay. It has a certain balance in it that helps the slip that comes in contact with the plaster dry at a reasonable rate to hold onto detail. I use Ceramic Earthenware Cone 04 slip. It is very inexpensive and bisque fires a clean white in the kiln.
Step 4: You've Made Your Own Bed...
To accomplish a 2 part cast you will need to first make a clay bed to hold your design while pouring your first half of plaster cast into your coddle board mold. I simply hollow out part of the clay rectangular shaped bed, so it fits nicely between the coddle boards, in the middle and lay my design roughly half way into it. Then I work my way around the edges of the design to ensure I have a nice tight edge between the design and the clay bed. You do NOT want plaster sneaking underneath your design. In the first picture you will see how tight the clay bed is to one of the arms of the cup we are using as a design.
Once you have your design snuggled tight in its clay bed place and clamp your coddle boards tightly around the clay rectangular bed. Once that is done go around the gaps of the coddle boards and bed with a coil of wet clay to seal the cracks and keep liquid plaster from sneaking out.
REGISTRATION KEYS! This is also when you will make 1/2-1 inch divits in you clay using your thumb around the design into the clay bed. This is shown in the third picture of this step and is very important to ensure your two parts of cast align each and every time.
We are almost read to mix plaster!
Step 5: The Secret Formula
My yellow note on the secret formula may not be of any help to you so I will explain it better here...
As the artist you can either choose to weigh your water or measure your water for volume.
1 Gallon of water = 9 pounds of weight = 231 cubic inches.
Now we need to know how much your overall volume for plaster was.
Lets do an example equation to help illustrate the following are the numbers needed to pour the plaster and create the mold for the Art Room trophies
Total Volume = 710 cubic inches (That is how much liquid plaster I need for both of the 2 parts of the cast)
710/2= 355 cubic inches (that is the amount of liquid plaster needed to pour the first half of the cast, the same number will be used for the second half)
We know that 1 gallon or 9 pounds of water = 231 cubic inches
355/231= 1.53 gallons or 13.8 pounds of water
We know we need 1.53 gallons of water to fill one half of our plaster cast... however that would leave no room for the actual plaster... which is used roughly 50/50 in our mix.
So you actually need to start with half of the water amount and so for our practice equation .75 gallons of water to put into our mixing bucket.
All that math...
Step 6: Mixing Plaster
Now that we have the amount of water we need to start with to create half of our plaster cast we can mix up our powdered plaster to a smooth silky chocolate milk consistency.
1 Use a dedicated plaster mixing bucket
2. Also add your water first then sprinkle in plaster slowly
3. DON'T MEASURE PLASTER... I simply sprinkle it into the standing water in the plaster mixing bucket until it "Islands" that is it creates an island in the middle of the water that doesn't sink below the water surface. It takes a little time to get to this point but it is very consistent and has always lead to great results.
4.Mix plaster by hand from the bottom up removing all clumps and trying not to work in air bubbles.
You've done it you have liquid plaster for pouring a cast!
Step 7: Clean Up Plaster
Before you pour you liquid plaster into your coddle board mold use a spray bottle and paper towels to clean you arms, hands, and mixing bucket into a trash can.
DO NOT PUT PLASTER IN YOUR SINK OR OTHER PLUMBING. IT WILL RUIN IT!
Step 8: Pour Some Plaster on Me...
You're coddle boards are prepped, your plaster is mixed and now you are ready to pour.... but WAIT!!
Before pouring plaster ALWAYS brush on a coating of a releasing agent. I use Murphy's Soap Oil watered down to a 50/50 ratio and coat the design, clay bed, and inside of coddle boards before pouring plaster. This helps the plaster release from the surface of stuff you don't want it sticking to.
Next pour your plaster... try not to splash it and pour it smoothly into your coddle boards. Also tap the table a little to work out any air bubbles that may have been caught during the pour.
.... now we wait.
Step 9: ...
and wait... and wait.
Step 10: ..3 Hours Later
The plaster will harden during this time and will feel warm to the touch during the process. After roughly 3 hours, or longer, depending on size of your mold, pop off your coddle boards flip over the plaster half and clay bed, remove the clay bed, leaving your design in place (it should be half buried in hardened plaster at this time)
Replace your coddle board, fill in the gaps with a clay coil again, mix your other half of liquid plaster following the steps above and pour your second part of your mold. DO NOT FORGET TO FIRST APPLY A RELEASING AGENT AGAIN. (This step in your Instructable is brought to you by Murphy's Soap Oil... Murphy's Soap Oil we'll release your plaster)
...again we wait.
Step 11: Houston We Have a Mold
After waiting for your second mold half to dry you can now remove your coddle boards, clean off the clay coil seals, and pop the two halves apart.
At this point I let my plaster cast dry for a few days. Plaster absorbs the moisture from the slip when it is poured into the mold so having it dry increases drying time and detail retention.
If you are in a rush, like I was, and have access to a kiln putting the plaster mold in the kiln at 160 degrees for 12 hours really speeds up the process. Just don't fire to hot because it will ruin the plaster.
Step 12: It's Dry! Time to Pour!
Make sure you mix your liquid slip really well it will also have the consistency of chocolate milk.
Using rubber bands, clamps, or tying it together put both halves tightly together using the registration keys you made during the pouring process. KEYS are KEY.
Once the two parts are together pour the slip in the top of your plaster mold as filled as you can. Any little gaps inside the mold will be filled by slip and create a nice seal so your first slip pour is never your best. .
So what is actually happening during this process?
Welp I am glad that you asked. When liquid slip is poured into dry plaster the plaster mold begins wicking moisture away from the slip almost instantly. This causes the slip level to drop for a few minutes so I suggest topping it off a few times. The longer the slip stays in contact with the plaster the thicker the slip wall is that is created while the plaster drys it out.
I have found 30 minutes is roughly my favorite time to have the slip walls thicken inside the plaster mold.
After 30 minutes its time to pour...again.
Step 13: Pour Out Liquid Slip
After 30 minutes or so the slip will have created a nice shell inside the plaster mold. Flip over your plaster mold and drain out the remaining liquid slip into a bucket to be reused. Think of it like a Cadbary cream egg with a chocolate shell. You'll drain the inside and the shell remains.
After it has been drained let the slip shell on the inside dry for a few more hours. Again depending on size I aim for 3-4 hours.
Step 14: Pop Out Your Slip Cast
After the drying time has passed separate your two plaster mold halves. Reminder your first pour will be a little rough because slip will fill in ever little crack but that is a good thing down the road. You'll notice some smoothing will need to be done in the picture. The slip is still at a "leather hard" stage at this point and is very easy to work. Take your time to clean up any issues.
Step 15: Ta-Da Organized Dust Sculpture...
IMPORTANT- After you have smoothed your slip cast out and let it dry from "leather hard" to what is called "bone dry" you'll notice the clay is much lighter in color and weight... it is also very FRAGILE at this point. It is just organized clay dust so be very careful until you bisque fire your slip casts.
Step 16: Bisque Fire
Bisque firing is the step in the ceramics process that converts earthenware to stoneware. We used Earthenware Slip 04 so we will be bisque firing it to a temperature of 04... also temperature is ceramics is measured on a scale called "Cone" that was developed by early ceramics pioneers in which "cones" would melt at a certain temperature needed for different phases of the firing process.
So we shall fire these trophies to Cone 04 and it takes roughly 20-24 hours till you are able to remove them from the kiln.
DISCLAIMER- I realize a kiln is a huge luxury to have and not many folks have one laying around however local schools and shops are sometimes willing to allow you to use theirs from time to time if you ask them. I have done this in the past. Not including the kiln slip casting is a fairly inexpensive process.
Step 17: That's Bisque Baby!
After 24 hours your Cone 04 slip cast trophies will come out Stoneware fired and look sturdy. They will feel a lighter in weight but they are much more durable and solid in the hand. You can repeat this process many times with your plaster molds and kiln to create hundreds of slip cast... anything!
On to finishing!
Step 18: Finish
Bisque fired ceramics are porous, meaning they have tiny little holes all over it that absorb liquids (think of a coffee cup without the glossy finish) if you want to paint ceramics, in this case gold, you will first need to Glaze Fire the stoneware to make in nonporous.
In this case I used a simple clear coat glaze. I dipped all the stoneware trophies and then fired them at Cone 05. This process makes the stoneware nonporous and also gives it a smooth shiny finish.
Now that the trophies are finished you can paint them any color you want. I used 3 coats of metallic gold, for that classy look... obviously.
Step 19: The Base... Is Basic
Since this is an Instructable about slip casting I will touch on the trophy base very briefly.
The base is scrap MDF I cut into circles and wood glued together. I then painted them with 3 coats of black spray paint... simple.
Step 20: Wrapping It Up
To attached the Golden Art Trophies to the base I drill a few holes into the MDF. This way the 5 minute loctite epoxy I mixed to adhere the ceramic trophies to the base would be able to have as much surface contact with the MDF as possible. It worked great and holds very well.
Step 21: You're Done!
These trophies came out awesome is such a short amount of time. They are sturdy, hefty, and look great. If you have any questions or make something with slip cast process please comment and leave pictures.
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In Metric the calcs are a bit simpler.
1 litre of water = 1kilogram = 1000 ml
Volume is WxHxL in this case 710cu in = 11.64 litres for both halves. So 5.8 litres per half.
We know 1kg = 1L so you need 5.8kg of plaster.
We know the water to plaster ratio is 50:50 so you need 2.9 Litres of water. And you'll be adding about 2.9kg of plaster.
But mixing process will give you the proper exact amount - but for purchasing this is useful info.
How do you get the the item "....half buried in plaster...?"
When the design is in the clay bed and you pour your first half of your liquid plaster that plaster hardens up and when you flip it over to remove the clay bed the design is half covered in plaster from your first pour. So it looks like it is buried.