Make a Simple Plaster Mold for Slip Casting

In this video I show how to make a simple one part plaster mold for slip casting. This is a great way to make your own first mold. I show how to pick out a form, how to measure out the plaster and mix it up, and finally using the new mold.
This is the second in a series of videos where I'm going to do a deep dive into plaster mold making for slip casting. We'll iterate through different approaches with the end goal of creating some software that can do most of the hard work of mold design for us!
TOOLS & MATERIALS (affiliate)
- 1 Gallon Buckets (plaster form) amzn.to/3OTcQ3o
- Drill Attachment Mixer amzn.to/3OP9iiv
- Murphy Oil Soap (mold release) amzn.to/3MQEWtm
- The Essential Guide to Mold Making & Slip Casting amzn.to/3OV2TCw

[@bunch8]

This is a good example showing another advantage of using metric for these calculations. Converting from mass to volume is a breeze. Nice summary of a simple mold. Thanks Ken.

[@PotterybyKent]

For water it is for sure! And it just happens to work out very well for getting the needed amount of plaster.

[@44oaks]

Just be a normal human being and use metric for everything.

[@Cassidy-po3ud]

For some reason, I couldn't leave a reply. I thought this was a good video, loved that you included a way to figure out how much plaster mix to use for the mold. I had wanted to reply about a substitute for Murphy oil soap. I saw someone from Australia used Walker Ceramics Soft Soap. (That's all I know about it.)

[@PotterybyKent]

Thanks! From what I understand, any non-detergent soap without extra additives should work.

[@theabristlebroom4378]

oh, I love your explanation about draft angles! Nice, clear visual demonstration! Your very dry "That's a bad day." made me laugh.

[@PotterybyKent]

Haha. Thanks! And yes draft angles can be a bit tricky to think about so glad to hear my explanation was clear.

[@tatendamapisire1597]

keep up the great work you are doing

[@PotterybyKent]

Thanks so much!

[@sheenalittle4246]

This is brilliant. Thank you so much I will give this a go 👍

[@PotterybyKent]

That's great!

[@pisdihly]

Amazing

[@PotterybyKent]

Thanks!

[@barkleyhunt9004]

thanks great video

[@PotterybyKent]

Thanks!

[@user-to9uz6ck3e]

Hi Thank you for your tutorial. I am interested in making some moulds for concrete plant pots , I intend to use a mix of white cement, plaster of Paris and white sand. Do you think a plater mould would be adequate for this concrete mix or I should use silicone moulds ??. Thank you

[@PotterybyKent]

I don't know anything about concrete planters. This channel is about ceramics.

[@scrapbooksiren1608]

I have vintage molds from 1978. 2 piece molds held by rubber bands. I used to cast low fire ceramics cone 06 and fire in my kiln but now live where I can’t use my kiln. I cast some yesterday with high fire slip cone 10 and it’s not releasing. These were molds I’d miniature food. Not sure I’m saying this right but does the cone of the slip make a difference in the release in the molds? Does low fire have less grit than mid or high fire?

[@PotterybyKent]

I'm not an expert in clay body materials, but yes they do have an impact. When I started, I was making slip from cone 6 throwing clay and often those parts would be "sticky" and not easily release. So I don't think it's so much the firing range, as it is the overall composition of the clay itself with the different types of component clays (which also change with firing temp).

[@loganwintry9945]

Did the sides cure faster than the inside? I'm confused on how that didn't form a solid block and instead got a near perfect pot

[@PotterybyKent]

The plaster is absorbing the water from the slip which results in the slip depositing on the edges. That the magic of slip casting and plaster!

[@szyszynka1189]

Any idea what else could be use instead of murphy soap? It’s not available in my country

[@PotterybyKent]

I'm pretty sure you want a non-detergent liquid soap (so one made without artificial chemicals). However if anyone here in the comments knows of alternatives, I'd be curious as well.

[@beverleybender1814]

I want to pour a mold to match my Rosenthal Baroness China bowl, what slip do I use for this fine china?

[@PotterybyKent]

No idea. Companies often use clay / slip that they design themselves.

[@beverleybender1814]

@@PotterybyKent

[@ZIZOCR]

Hi! thank you for tutorials! I have a question! I dont have access to morphy oil. Is there anything as a replacement? For example, olive oil?

[@PotterybyKent]

I do not know what else might be commonly used, but it is a soap. So if you were to try an alternative, maybe liquid soap.

[@ZIZOCR]

@@PotterybyKent thank you 😊 🙏

[@epidian6240]

Mydło szare ( kostki zetrzeć na wiórka) włożyć do garnka dodać mydła technicznego i gotować razem co jakiś czas mieszając po ostudzeniu dodać olej może być maszynowy i wszystko miksować do konzystęcji majonezu. Proporcje dwie kostki mydła szarego wagi 200 gram każda woda około 0,8 litra i technicznego 100 gram gotować około 3- 4 godzin

[@Cassidy-po3ud]

I saw someone from Australia used Walkers Ceramics Soft Soap. (I don't know if that helps you, but that is what I have seen.)

[@karenleguilcher3956]

Hi Kent From where did you get the stirrer

[@PotterybyKent]

It's this one: amzn.to/3R4hRGK

[@ryancarlson5838]

What kind of plaster. The art plaster I can buy locally seems quite soft. Is it a special kind of plaster?

[@PotterybyKent]

It is USG number one pottery plaster. It is specifically designed for ceramics applications. I'd recommend going to a ceramics supply store - they should have it (or the local equivalent if outside the US). Beyond that, as far as hardness goes, one of the factors influencing the strength of plaster is how hard it is mixed (more vigorous leads to harder plaster).

[@meggysuitiful]

If your plastic container has a plastic label you can't remove , will that be an issue? It wouldn't seem so once the plastic was coated with wood soap.

[@PotterybyKent]

If it protrudes from the surface, even a tiny bit, then that would likely transfer into the plaster (and your pot). But as a way to get started I'm guessing it would be good enough.

[@meggysuitiful]

@@PotterybyKent The kind I refer to are sprayed on so appear to be part of the container. I'll give it a try! Thank you.

[@englishnerd2243]

So, when the final product/planter dries, it just sets out at room temp? For how long?

[@PotterybyKent]

You let it dry until it is bone dry - how long depends on the piece and your temperature/humidity/etc. You then bisque and glaze fire it to turn it to ceramics just as if it was made with hand building or wheel thrown.

[@englishnerd2243]

Thank you for your speedy response Kent! Do people often "rent time" at places that have a kiln? This is all so new to me. Thank you!

[@PotterybyKent]

Sure thing! Yes, some pottery shops and studios will rent out space in their kilns. There is also www.kilnshare.com/ And likewise you can join a studio to take lessons or do pottery there.

[@epidian6240]

Formy obrotowe robi się na kole , szkoda że nie masz. Ja już od 20 lat zajmuje się robieniem form gipsowych do odlewu i formowania ceramiki zawodowo

[@PotterybyKent]

I like my process!

[@epidian6240]

Dokładnie radzisz sobie dobrze ale można lepiej, czy umiesz zrobić foremkę na czajnik , albo formę do bateryjnego odlewu uszek do filiżanek czy kubków

[@SprayGuitar]

What if your cup doesn’t float ? 😂

[@PotterybyKent]

If it captures the air pocket inside, it will float for sure!

[@SigridVerbert77]

You lost me at the air compressor 🙄

[@PotterybyKent]

Try it without. I only use it occasionally. Some forms are easier than others.

[@SigridVerbert77]

@@PotterybyKent Thanks for your answer, I'll give it a try then! Also, I was wondering if I could try and cast a glass shape? (did I miss the part where you talk about that?)

[@PotterybyKent]

Check out my two part video in the playlist!