#slipcasting — Public Fediverse posts

Here's a question for potters and/or chemists and probably a lot of other people too.

Pottery plaster is mixed with water at a 10 to 7 ratio. That is e.g. a kilogram of dry plaster wants 700 grams of water. Similarly a basic recipe for refractory molds for glass casting is half dry pottery plaster and half silica flour with a dry ingredient to water ratio of 3 to 2.

The problem lies in predicting the volume of liquid plaster produced from a given amount of water and dry plaster. There's a lot of miscibility going on and it's not even close to the sum of the volumes. Andrew Martin* has a recipe that gives one quart of wet plaster and using the ratio it's easy enough to scale it up or down as needed. But there's no such recipe for the glass casting mix, and anyway using a recipe bothers me to some extent -- e.g. how will I figure amounts if I want to fiddle around with the ratio?:What I'm looking for is a direct way from "I need x milliliters of wet mix so I should use y milliliters of water" and then use the ratio to calculate the amount of powder.

So what occurs to me is this: barring technical and irrelevant details like elevation about sea level and air temperature the specific gravity (= weight in grams of one CC) of each of these two mixes ought to be constant. Suppose way pottery plaster has a specific gravity d. Then if I need e.g. v cubic centimeters of mix I know I need vd grams of mix. If w is the amount of water I need and p is the amount of plaster, both in grams, then we should have:

w+p=vd
7p=10w

So 0.7p=w and therefore p=vd/1.7 and w=0.7vd/1.7.We can do something analogous with the plaster/silica recipe. A formula like this would be much easier to work with since d is constant so I could get the amounts directly with just two calculations.

My question is: will this work? I'm worried a little about the assumption that the weight of the wet mix is the sum of the weights of the ingredients. There's some kind of chemical reaction happening with the water and the plaster and it wouldn't be all that strange if some weight was gained or released at that stage e.g. if some atoms are related or absorbed. The thought of mixing and measuring accurately enough is daunting so I thought I'd ask fedi!

*If you want to learn slipcasting Andrew Martin's book The Essential Guide to Mold Making & Slip Casting is fantastic.

#Ceramics #Pottery #Slipcasting #MoldMaking #Plaster

I made a gallon of porcelain slip yesterday and today a gallon of terra cotta slip with one pound of kaolin and nine pounds of redart. Lesson learned? Don't touch the wet redart for any reason! The manufacturer's spec sheet says it's messy and oh my God what an understatement! It sure is pretty, though!

#Ceramics #Pottery #SlipCasting #RedArt #Porcelain #SlipMixing

Here's the model I used for the mold. It's a plastic pencil holder. The shrinkage was over 18%. Also a picture of the mold itself. You can see ghosts of the colored slip trails I splashed around in it before filling it with casting slip. Casting plaster is really an amazing thing!

4/3 (really the end)

#ceramics #Pottery #Slipcasting #Porcelain

These are so thin that they're translucent at cone 10, which is something I never thought I'd be able to do!

Now I'm on to the next phase, which involves sprigs and very tiny pieces of glass melted onto various parts of the outside. More news when I have it!

3/3

#ceramics #Pottery #Slipcasting #Porcelain

I made press molds from some Czech glass buttons I had laying around and used those to decorate the bottom handle attachments. These are a little blurry, but so are the originals.

2/

#ceramics #Pottery #Slipcasting #Porcelain #CzechGlass

A couple years ago I had a vision of a porcelain mug but it was far beyond my skills at the time. At the beginning of this summer I finally felt like it was within my grasp so I started learning the necessary skills. Slipcasting was the most complex but two months in I feel like I'm good enough at that to move to the next phase. Here are a couple of slipcast mugs I finished yesterday as proof of concept. The decoration isn't what I ultimately want, but it's beautiful in itself and I thought I'd share.

1/

#ceramics #Pottery #Slipcasting #Porcelain

we played around a bit with some underglaze and carving. not entirely happy with the carving as it is a lot deeper than expected but the mudtools carving tools do cur really well.
underglaze will probably fire pretty translucent but we’ll see

#pottery #slipcasting #underglaze #carving

- our 2nd slip casting went a lot better
- dry mold
- 1 hour soak time
- solidifying in covered mold overnight
- it came out nice and leather hard, easy to handle but still workable


#pottery #slipcasting

a continuation of our slip casting experimentation. After not wanting to come out of the mold all day yesterday, this very thin walled bowl dried to bone dry in just a few hours, cracking in the process.

it does not seem like the mold was sufficiently dry, resulting in the thin wall thickness and extremely slow drying in the mold, we have put to mold in a warm place to help drive off more moisture

#pottery #slipcasting

busybee: Notes: Plaster slip casting notes https://beesbuzz.biz/blog/chatter/14199-Plaster-slip-casting-notes #SlipCasting #3DPrinting #Notes #Blog #Wiki

Dog Bowls Show the Versatility of Ceramic Slip Casting - Here at Hackaday, we feature projects that are built of just about every material imaginable. Sili... - https://hackaday.com/2021/01/03/dog-bowls-show-the-versatility-of-ceramic-slip-casting/ #slipcasting #lifehacks #ceramic #plaster #how-to #clay #mold #slip