Two Piece Plaster Molds By Kristen Wilson by Kristen Wilson

Mold for Menat

kwilson47 — 2015-11-14 16:31:31 UTC

Egypt, New Kingdom-Late Period, 1550-333 B.C. Tools and Equipment; molds Clay, Terracotta Gift of Jerome F. Snyder (M.80.202.10) Egyptian Art

Source: http://collections.lacma.org/node/244948

First Step

kwilson47 — 2015-11-14 16:38:20 UTC

Make your clay coin. Place a coil, exactly at the half way mark on the thickness of the coin. Place clay or any resist around the original clay coin. Pinch a coil around the clay mold, so plaster will not leak out.

Three different double sided coins

kwilson47 — 2015-11-14 16:58:00 UTC

Ready for plaster

Student work

kwilson47 — 2015-11-14 16:59:23 UTC

Three double sided student coins

Close up of student work

kwilson47 — 2015-11-14 17:01:29 UTC

Notice the plastic bag placed underneath the molds. This will help catch any plaster and make clean up easy.

Pour the Plaster!

kwilson47 — 2015-11-14 17:04:43 UTC

Mixing pottery plaster is very specific, and it is very important to read and understand the instructions on the plaster bag you purchased. Read and review safety instructions.

Patience with Plaster : - )

kwilson47 — 2015-11-14 17:06:27 UTC

Temperature of the air and the water can effect plaster.
Water to plaster ratio is very specific.
The way you scoop up your plaster is also important, avoid scooping into a bag, the plaster gets compacted so the amount you are measuring could be inaccurate.
Instead, sprinkle the plaster into your measure cup.
I found it difficult to estimate the exact amount of plaster I would need, so I did my best calculation and found containers to pour the excess into. I ended up making some wonderful Pukis as you can see in the red containers below. The pukis or “the supporting mold, a dry or fired clay shape where a round bottom of a new piece may be formed” builds the base shape of a rounded pottery shape.
Watch Maria Martinez here: @ time: 4:30 in this video: https://youtu.be/M18b6XMB81o
More about Maria Martinez : http://millicentrogers.education/inventor-scientist/

One side is now complete.

kwilson47 — 2015-11-14 17:12:13 UTC

Carve out three notches, or keys, where the two molds will fit together.
Another form now needs to be created around this newly created one sided plaster form to create the other half of the coin.
I re-used as much of my previous form (clay) as I could, although I needed more clay to create the second side of the mold.

Soap acts as a resist, place a thick layer on the top of the first plaster edge, before you pour the second mold over the first.

kwilson47 — 2015-11-14 17:37:00 UTC

If you compare the previous image with this image, you will notice there is no hole in the coin. When I created these, my intention was to have a hole in the coin, so perhaps a ribbon could be added. Above you can see I tried to make the hole in the plaster mold. This was tricky, and unstable. I broke off that plaster, then sanded it down smooth. In the leatherhard stage of clay, I pushed a sharp long wooden tool expanding the hole approximately 1/4 inch.

Two plaster molds completed

kwilson47 — 2015-11-14 17:51:04 UTC

Prying apart the mold takes patience. When to begin to break the mold apart from the first mold I found challenging. Not waiting long enough will beak the entire mold. Waiting tool long makes the job of chistling tough.

Working with plaster

kwilson47 — 2015-11-14 17:54:09 UTC

is hard! But with practice comes mastery. You can see here in this image there where bubbles formed, then hardened. Thoroughly mixing the plaster is key, as well as temperature and ratio of water to plaster.

Completed two piece mold and original clay coin

kwilson47 — 2015-11-14 17:57:37 UTC

This was a better mixture of plaster as you can see there are less bubbles and holes

Plaster imperfections

kwilson47 — 2015-11-14 18:05:19 UTC

The plaster did not hold up perfectly in my design as you can see at the top of the letter "L" and the middle of the "G". Notice the lower level of the scalloped plaster edge detail around the outside of the circle reproduced perfectly, however, the higher L&G letters did not mold as well.

Finished plaster pieces

kwilson47 — 2015-11-14 18:21:45 UTC

The coin molds are kept together with rubber bands. Plaster can absorb moisture, so keeping the two pieces of plaster banded tightly together prevents any warping.

Look at the numbers, each plaster mold must be lined up with the number to fit together.

Finished glazed coins

kwilson47 — 2015-11-16 14:04:45 UTC

Soon I will add a slide of the finished glazed coins...