Improved - a One Part Plaster Mold for Slip Casting

In this video I show how to make a some improvements to create a better one part plaster mold for slip casting. This builds off of our last video where I showed a very simple way to get started. In this video we add a slip well so we get a cleaner rim, and pour the plaster upside down so we are less likely to get bubbles in the faces needed for slip casting.
This is the third 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
- Bar clamps (for cottle boards) amzn.to/3X2HZTV
- Hot wire foam cutter (for slip well) amzn.to/43QoFeL
- The Essential Guide to Mold Making & Slip Casting amzn.to/3OV2TCw

[@liarspeaksthetruth]

About every 11 seconds you provide a nugget that pays for itself (and, honestly, a couple of classes). If you're not a tenured teacher somewhere, you should be,. Many thanks for the great instruction.

[@PotterybyKent]

Thanks for the feedback! It's much appreciated. I do occasionally think about becoming a prof one day, but time will tell!

[@SprayGuitar]

Nice vid! If you just throw the circle that you’re attaching the pot upside to on the wheel, then you can stick the pot in slightly and have no under cut. And use green ware cups for casting, then you can break the cup inside the mould for no chipping

[@PotterybyKent]

That only works if you have a wheel!

[@dolittlelane]

Lovely, thanks for sharing 😻🐦

[@PotterybyKent]

Sure thing!!

[@patriciakoenig3966]

I enjoyed your video especially all the little details😂❤❤❤❤

[@PotterybyKent]

Thank you so much 😁

[@diananesbitt1260]

I don’t know if you know this but you can repair where the chipping appears to a perfect finish. When you take a little plaster and mix with water to the consistency of whole milk it will come one with the chipped mold. I drop a tiny drop into the air hole after teaming out to make the opening larger. I drop however many drops it takes to fill it perfectly level. You cannot tell that you’ve done it because it is all solid. I do this with molds that have chips in the detail. I have mended pretty big areas down to tiny. It works every time. If you over fill the damaged part while it is still damp scrape it level as you would scrape the edges to take off the sharpness. Also, when I’m preparing the plaster for making the mold, before I pour it into the outer mold, I pick the container up and drop it a few inches to make the bubbles rise to the top. I give it a couple slow stirs and that helps pop the bubbles. I pour it slowly. I, then, tap the sides a few times before it starts setting up to remove any more that may have thought they could outwit me! Crazy plaster! Let me know if this works for you.

[@PotterybyKent]

Thanks for sharing! Plaster does stick to itself very well! The problem I've had in the past is getting the surfaces flush. In particular I had challenges fixing bubbles at the bottom of the mold - probably because I can't really get my hand down in there and haven't really found any tools that worked for me. If you have any tips or tricks there, that would be great! And I've tried to tackle bubbles a few times on this channel! But yes getting them to release while still in the container, and shaking it afterwards both should help!

[@afranda]

Thank you!

[@PotterybyKent]

You're welcome!

[@theabristlebroom4378]

Kent, you can also fill the void inside of the pot with clay so that it doesn't float. BTW, I'm loving your evolution in skill, both in making molds, and in video presentations. You're about to take a leap forward on your channel, I'm certain. Good luck and bright blessings!

[@PotterybyKent]

Thanks a lot! Yes that's a good point about filling up the form to make it more dense. And thanks for the comments on my progression - it's much appreciated!

[@Tiny_Island_Designs]

You have saved me so much time and heartache. I was going to make a mold of a large glass vase I have but now I see I won't be able to lift it. I will do a press mold of it instead. Thank you.

[@PotterybyKent]

Glad to help!

[@reneroberts7875]

I’m such a novice but really want to make my own pots. The entire video I wondered how you got the center of the pot hollow. I was amazed that you dumped the slip out but there was still a thin layer that stayed. How did you figure out plaster would absorb just enough? How do you know when to dump the slip? And if you leave it longer before dumping will the pot be thicker? Got to love science.

[@PotterybyKent]

Yep - it's a pretty cool process! You are right in that the thickness of the pot created is based on how long the slip sits in the mold (and a bunch of related factors). I let mine sit for 25-30 minutes and if you're just starting out pick a time and wait. If the pot is too thin, wait longer next time and vice versa. The clay can be recycled over and over before being fired by just adding the water back.

[@Olliexuxunugget]

Hi Kent! Love your videos. Would you share the type of clay you use for your pieces ?

[@PotterybyKent]

Thanks! I use a dry porcelain-like mid fire casting slip produced by my local pottery shop. shop.clay-planet.com/dry-icelia-porcelain.aspx There are similar products by the big brands as well.

[@keithlightminder3005]

Option 1. One can swain the slip by patrolling the many plaster molds and topping them up regularly. Option 2. I’ve seen a well big enough above to prevent the dropping rim. Option 3. Another is make a plumb, stake and chocks set up. Throw a solid cone which is about 3cm or more away from the sides and bottom, while it’s on the wheel head drive a stick or chopstick through it at about 1.5 cm from the wheel head horizontally and wiggle it so it won’t shrink-crack the cone. Next make little bricks with half cylinders crossing the top, short span. Make these in pairs at different heights, about 2cm difference each from the last. They need to be at least a 1:3 width to height ratio so they don’t tip. As the slip shallows put the upside down cone up on blocks until the liquid is level again as the slip is displaced by the volume of the cone. Lower to lesser blocks to keep it up. Let them dry fully then fire. This is every bit as consuming and a choice to swain the slip, and clutters up the tool shelves. Some working with large pots prefer this for ease of making less slip ready. I’ve also seen molds under a rafter with strings and Water filled glass bottles hung over and guided by thumb tacks on the side of the rafter, and all the strings came together onto a wooden spoon that was occasionally being moved from hole to hole up the side of a workbench. It also kept the level up, but if something had gone wrong it would have gone consistently wrong.

[@PotterybyKent]

Thanks for listing all of the alternative methods! I hadn't heard about the displacement method before. I am all for letting the mold do the work for me but those are interesting for sure. I could also imagine for big molds the displacement approach would be very handy - less slip needed to wrangle!

[@kathypowell8892]

Thanks, Kent, great video. I want to use a vintage wood bowl as a mold. Do you think the plaster would ruin the wooden bowl?

[@PotterybyKent]

Thanks! It is quite possible it would - you'd probably want some sort of protective coat if you tried. The other potential issue is the final pot would be smaller than your bowl.

[@rochellebrandon2547]

Hi Kent, Love the videos. How do you cut your pink foam so that the edges are so smooth? I’ve used a craft knife and the edges are rough making a rough top edge of the mold which is a nightmare for slip casting. I had to discard my first mold. I don’t have a 3D printer or software, but I aspire to get to that level. Any specific recommendations would be appreciated.Thanks in advance! Rochelle

[@PotterybyKent]

I used a foam hot wire cutter. You could also search for a foam hot knife. Basically they heat up and melt the foam instead of cut it. You can also just sand away the rough spots as well.

[@rochellebrandon2547]

@@PotterybyKent thanks. I’ll look for one at the hardware store

[@CarisseH]

I am wondering what would happen if you had the second batch of plaster ready to go, by just having the plaster soaking in the water without mixing yet. Could it sit like that while you mix the first one and pour it into the box? Then mix after your finished with the first pour, this way it might decrease the chances of a pour line. I am really curious how that would work out.

[@PotterybyKent]

That's a good question. Luckily plaster is really good at sticking to itself so it's probably not going to be an issue. But the less time you have between the two is probably for the better

[@CarisseH]

@@PotterybyKent If you do end up trying it out, I would like to know how it works out.

[@stigdybdal6872]

Do you Wash the form befor casting ? Thinking about the soap you used to make the form? 😊

[@PotterybyKent]

If you use it, then yes it's a good idea. At this point I don't need it with my molds at all though using my mold system, Shape Cast.

[@drjmansplace5174]

Ever tried using cooking oil for mold release?

[@PotterybyKent]

I have not. However at this point I'm not using any mold release with my mold system and it's working great.

[@kibibu]

When the slip goes down, ya better be ready (when the slip goes down)

[@user-rn8xn4nh5t]

What kind of foam are you using? :) Thanks!

[@PotterybyKent]

It is extruded polystyrene

[@user-to9uz6ck3e]

How can you control the wall thickness of the casted pot ?

[@PotterybyKent]

The longer you let the slip sit int he mold, the thicker it gets. That rate is really dependent on your slip, paster mold, and form so the best way to test.

[@user-to9uz6ck3e]

how do you make your own slip ?@@PotterybyKent

[@PotterybyKent]

To start, I recommend buying it premixed. Otherwise, I have other videos here showing my process - basically dry clay made for slip, water and deflocculant.

[@catherinelikesflanne]

Does the tape need to be foil tape?

[@PotterybyKent]

Others might work, but it would need to have similar characteristics - water resistant, strong enough, and then be able to be removed. (I've stopped using tape now that my mold system is working).

[@epidian6240]

Mogę nauczyć jak robić formy gipsowe , czekam na zaproszenia

[@PotterybyKent]

I'm doing just fine making plaster molds, thanks. If you have any specific tips on how to improve my mold system, I'd be curious.

[@epidian6240]

Podaj maila , ja pracuję jako modelarz w zakładzie produkującym porcelanę . To co robisz można zrobić prościej i szybciej . Nigdy jeszcze nie spotkałem się z wydrukiem 3d kubka czy filiżanki aby był idealnie prosty i zrobię szybciej model kubka i foremkę niż drukarka 3d

[@PotterybyKent]

You're assuming goals I do not have. As for 3D printers, I recommend looking harder.