How to Make A Lot of the Same Thing:
Making Jello Parts from Clay Molds
Many products that you use every day are molded. One of
the simplest examples of a mold is an ice cube tray. The shape of the
tray is the negative (opposite) of the shape of the ice cubes. You
pour water into the tray and put it in the freezer until the water
solidifies. Then you can remove the ice cubes. In this case, the
product is the ice cube and the ice cube tray is the mold.
In general, a mold is the negative
of the part that you want. Liquid material is poured into the
mold. The material hardens in the mold and then is removed. Like
the ice cube tray, most molds are reusable so you can make as
many reproductions as you want.
Most plastic products, like the cases for VCRs, TVs,
telephones, and computers are molded. So are many foods, like
gummy bears and Popsicles. Making complicated parts, like the
cover for a VCR, often requires a mold with more than one part.
After you are done making molds today, you will be able to look
around at the things in your house and in the grocery store and
figure out whether they were made using molding.
Supplies:
Jello, clay, paper towels, plastic cup, a ziploc
bag, and an object to reproduce.
Step 1
Pick an object to duplicate, like one of the Lego pieces that we
brought to class.
-or-
Think of something to form a mold of your own.
Step 2
Form your clay into two blocks. The size of your
clay blocks depends on the size of the object you pick. Each
block should be about twice the size of your object.
Step 3
Take a look at the object you are going to reproduce. One of the
requirements for molding is to be able to get the part out of the
mold. We picked objects that are straight in at least one dimension
so they will be easy to remove. In class, we will talk about how to
decide which way to put your object in the mold. (If you look at an
ice cube tray, you may notice that the sides of the cubes are slanted.
The slant is called a draft angle and is there to make it
easier to get the ice cubes out.)
Push the object half into one block, then place the other block over
it and squeeze the two together. This is called making an impression.
Use your fingernails to make a line that crosses
both halves of your mold. Make a line on each side of the block
so you will be able to line up the mold before you pour the liquid
in.
Step 4
Separate the halves and take the object out slowly and carefully.
Make sure the two faces are flat so the mold will fit together
well.
Step 5
Spray Pam onto the inside surfaces of the mold. Pam is our release
agent, which will allow the Jello part to come out of the mold
more easily. Hold the can 12 inches away and spray a short burst. If
there are pools of oil, dab them with a paper towel. It is important
to not have too much because then the Pam will mix with the Jello and
it will not set properly.
Step 6
Reimpress the object to perfect the mold. The more carefully you make
the impression, the better the results.
Step 7
Use a pencil or other round object to make a channel for the Jello to
flow through. This is called a gate. In class, we will talk
about some things to think about when you place the gate.
Step 8
Put the halves of your mold together, making sure that your marks line
up. Seal the halves together with clay. It is important to seal the
mold well so that the Jello will not leak out.
Step 9
Pour the Jello into your mold through the gate.
AT HOME:
Step 1
Place the mold in the refrigerator and wait at least three hours.
Waiting overnight is better, because this gives the Jello time to
harden.
Step 2
Separate the mold carefully with a butter knife.
Step 3
Carefully demold your part. Use a finger to pry
up one edge or hold the mold upside down to get your reproduction
out.
Heather Thompson and
Susan Finger <sfinger@ri.cmu.edu>