Introduction: Casting Plaster to Make a Pencil Holder
This is the instructable to make a plaster pencil cup. There might be someone who wants to have a pretty pencil cup from plaster. Even though the plaster can break if it falls hard to the floor, it is durable and can be used for a long time. We can choose some color to make it looks attractive as well!
Basically, you need these materials below:
- cutter knife
- cutting board
- stirring spoon
optional* food coloring
Step 1: Step 1: Plan Your Design
We need to choose a shape that is not boring but to have interesting forms and can still perform its function. I search up for 3D shapes, geometric shapes on google and found the shape of dodecahedron and icosahedron.
The dodecahedron's side is filled with pentagon 2D shapes as the sides, icosahedron's side is an equilateral triangle.
Then design your core, a thing that will be stuck inside to make a hole. I rather choose a simple one, just for holding a pencil.
Then search up for the nets.
Step 2: Step 2: Drawing the Design
After searching for the 3D shape nets, you can draw it on the paper card by measuring the size of the design. One side should be around 5-8 cm to not making it too big or small. You can draw just one perfect 2D shape and trace around the card paper.
For the core, the height should be around 8-12cm. If you are making the circle you need to use 2 x pi x radius to know the perimeter and roll the paper into the circle. Draw the circle with compass.
Step 3: Step 3: Building the Design With Card Paper
After you finish drawing the shape, you need to cut it by using scissors or a cutter knife. Fold it along the line you have drawn. Then tape the sides together. You should cut one side of the net to pour the plaster and put the core in. Then decide which one you like the most and want to create the pencil holder.
Step 4: Step 4: Making the Mold and Core
Decide which one you prefer. We are using polypropylene to make a real design. The card is not durable enough for pouring plaster so we use polypropylene instead, it is strong enough to hold the plaster. Do the same thing as you did for step 3.
Draw the net with a permanent marker onto the polypropylene, then cut it with a cutting knife or scissors. To fold it this time, polypropylene is a hard material. We have to use the cutter knife with the cutting board and cut it with 1/2 strength, don't cut all through. If it's successful, you should be able to fold the polypropylene without separating each 2D shapes. Then tape it properly so the liquid plaster won't leak out.
Make the core exactly like the card one.
Step 5: Step 5: Plaster Pouring
Making the plaster to pour into the polypropylene:
Mix the water with plaster powder by the ratio of 2:3 (water: plaster) into the bucket. Then use the stirring spoon to make the texture of the liquid look smooth and had no remaining.
You can add colors to the liquid by 20-30 drops.
This step needs to be quick because the plaster will dry quickly, no more than 3 minutes. Pour it into the mold carefully around 3/4 of the container. Quickly push the core to touch the bottom of the mold, then lift it up a little. Hold it for 30 seconds- 1 minute and tape over the core to make it stay and not sticking out.
Leave it to dry for at least 24 hours.
Step 6: Step 6: Finishing
After it dried, pull off the tape first. If it was successful, it should turn out to be a nice prototype! Then use your strength to pull the core off. This step will be a bit tough and you might need a buddy to help you hold the prototype. You will get a nice prototype but there's a chance that the hole edges might not be smooth so you need to file down.
Step 7: All Done!
Finished. You can customize or trim as desire but you got a complete pencil holder to use!