Attaching hand sculpted elements to a porcelain slip cast piece (is it possible?)

[kawaiidumpling]

Hello, 

My apologies if this is the wrong place for this post,

I'm very much a beginner but have taken two ceramic courses. They are not keen on teaching you about porcelain, which is why I thought I'd take matters into my own hands and teach myself, as it is the only clay type I'm interested in (even though I'm told it's too difficult for beginners, I'm stubborn and like it way too much not to start working with it). I want to try slip casting as an affordable wheel alternative and for a change, and would like to attach my hand sculpted pieces (tiny humans, animals, leaves) to, for example, a slip casted mug, to create some sort of fantasy scenery mug. I'd also like to paint details on them with homemade underglaze, and I wondered if it would be a good idea to make it out of the same clay used for the sculpted pieces. Dried, ground up and mixed with high temperature pigments in the right proportions, and then made into a slip.  But both the sculpted clay and the engobe would need to have the right shrinking percentage for the slip casting clay.  I can't find too much information about it online. Is mixing these two mediums possible or too much of a risk? The clays sold do come with the percentage.... but is it really this simple?
Could I dry out the pre-made liquid slip clay slightly, and use that for sculpting as well? Or will the slip ingredients make it less suitable to work with in that sort of way? Merely a matter of trial and error?Ahh! I have no idea....

[PeterH]

Do you have any porcelain clays in mind? What cone do they need to be fired at, and can you reach those temperatures? Mugs need to be waterproof, so you would probably need to fire to maturity.

If you made moulds from your sculptures you could slip-cast them in the same casting slip and apply them to the freshly cast mug, largely avoiding compatibility/shrinkage issues.  Easier if you restrict yourself to low-ish relief with no undercuts, but you could go the full multipart figurine route.

 

 

[neilestrick]

Hi @kawaiidumpling, welcome to the forum!

I feel you're complicating things a lot here, but to answer your questions:

Yes, the published shrinkage rate of a clay body is that simple. Ideally you would be using the same clay body for the hand built pieces as you are for the mug body, but if that's not possible then just find bodies that have a similar shrinkage rate.

If you buy pre-made slip, drying it to use for the hand built pieces is not recommended because casting slip is deflocculated and won't behave the same, although for very small things it may work. It could also be used for the engobes, but you'd either need to calculate the materials content of the slip or dry it out so it can be weighed. Rather than making your own underglazes, I recommend buying commercial underglazes. They tend to work better than homemade, the cost per pot is very low, and they can be blended for different colors and watered down for different effects. Making your own will require a lot of testing (which will need to be fired, presumably at your community studio) to get the color and intensity correct, and with the cost of stains you probably won't save much money by doing it yourself.

What do you mean by 'an affordable wheel alternative'? Are you just referring to the cost of buying a wheel?

Slip casting and mold making are entirely different beasts than throwing or hand building. Using slabs or coils to build your pieces would simpler and teach you a lot more about working with porcelain. I'm not saying casting is not a worthwhile endeavor, but slab and coil work would  build on the skills you've gained in your classes a lot more than slip casting would.

The difficulties your teacher are referring to come from the lack of plasticity, high shrinkage rate, and propensity for warping that comes with porcelain. All of these issues can be dealt with for the most part through good design and construction techniques. It's not really that different than working with stoneware, it's just fussier. Many of my students throw and hand build with porcelain, with great success.

[kawaiidumpling]

Quote

PeterH

thanks for the answer. I will look into the coning stuff. Hmm I would definitely prefer the hand sculpt method, but if it's not possible I might try making my own molds..... But I would have to make many different ones and some details would be a bit too small and simple to make a mold of , I think..  That and I also like the sculpting process. My local pottery webshop does have both liquid and solid porcelain from the same brand called witgert. But mixing the two is just not very common it seems. the closest firing place fires porcelain glaze at 1260 degrees celcius (2300 F).

Edited April 23, 2023 by kawaiidumpling

[kawaiidumpling]

6 minutes ago, neilestrick said:

Hi @kawaiidumpling, welcome to the forum!

I feel you're complicating things a lot here, but to answer your questions:

Yes, the published shrinkage rate of a clay body is that simple. Ideally you would be using the same clay body for the hand built pieces as you are for the mug body, but if that's not possible then just find bodies that have a similar shrinkage rate.

If you buy pre-made slip, drying it to use for the hand built pieces is not recommended because casting slip is deflocculated and won't behave the same, although for very small things it may work. It could also be used for the engobes, but you'd either need to calculate the materials content of the slip or dry it out so it can be weighed. Rather than making your own underglazes, I recommend buying commercial underglazes. They tend to work better than homemade, the cost per pot is very low, and they can be blended for different colors and watered down for different effects. Making your own will require a lot of testing (which will need to be fired, presumably at your community studio) to get the color and intensity correct, and with the cost of stains you probably won't save much money by doing it yourself.

What do you mean by 'an affordable wheel alternative'? Are you just referring to the cost of buying a wheel?

Slip casting and mold making are entirely different beasts than throwing or hand building. Using slabs or coils to build your pieces would simpler and teach you a lot more about working with porcelain. I'm not saying casting is not a worthwhile endeavor, but slab and coil work would  build on the skills you've gained in your classes a lot more than slip casting would.

The difficulties your teacher are referring to come from the lack of plasticity, high shrinkage rate, and propensity for warping that comes with porcelain. All of these issues can be dealt with for the most part through good design and construction techniques. It's not really that different than working with stoneware, it's just fussier. Many of my students throw and hand build with porcelain, with great success.

Thanks for the advice! 

The reason for wanting to make my own engobe is that there are no online stores in my country that sell colored slips for porcelain (or higher temperatures) as far as I'm aware. I looked everywhere but they were nowhere to find, so I impulsively ordered some pigments some months ago. An average electric wheel is over $2000 so I do see molds as the only affordable DIY option for now (ceramic season is over as well, so barely any courses available locally). 

[neilestrick]

30 minutes ago, kawaiidumpling said:

The reason for wanting to make my own engobe is that there are no online stores in my country that sell colored slips for porcelain (or higher temperatures) as far as I'm aware.

Most commercial underglazes will go to cone 6, many can handle cone 10 as well. The main issue with higher temps is the stain/pigments they use, and they use the same stains in them that are available for us to buy. Be sure to check the tech stats for each stain to see what temp it can handle. If you can find a good cone 6 porcelain that will open up a lot of possibilities.

35 minutes ago, kawaiidumpling said:

An average electric wheel is over $2000 so I do see molds as the only affordable DIY option for now (ceramic season is over as well, so barely any courses available locally). 

Yeah, wheels have gotten really expensive in the last couple of years. If you want to explore slab work you can do that with a rolling pin and some thickness strips, or tabletop slab rollers are pretty affordable.

[PeterH]

2 hours ago, kawaiidumpling said:

An average electric wheel is over $2000 so I do see molds as the only affordable DIY option for now (ceramic season is over as well, so barely any courses available locally). 

Still arguing for using the same body for mug and sculptures. If you want/need to attach hand-build sculptures, why not hand-build the mug.

101 on making a slab mug, with tips on rolling out the clay if you are unaccustomed to hand-building
https://thepotterywheel.com/slab-built-mugs/

Personally I prefer to  join round a tube of some sort, as in
https://clairepalmerphotography.wordpress.com/2014/05/13/how-to-create-a-cylinder-vase-slab-building/

[neilestrick]

You can also work in panels, like building a box. By using templates for the panels you get excellent repeatability.

 

[PeterH]

You could also make/buy texture sheets/rollers to provide a low-relief background for your sculptures.
e.g. https://www.etsy.com/uk/market/polymer_clay_texture_sheet

[Jeff Longtin]

A few slip cast issues to consider: as slip cast pots tend to be cast thinner than hand built/wheel thrown pots, most folks wait until the pot is bone dry to clean them.  "Underglazes" tend to have more non clay ingredients, in them, so they partner better with bone dry pots. "Engobes", which tend to have more clay in them, tend  to work better when applied to leather hard pots. Which you chose would depend upon when you intend to apply them to the pot/ceramic object.

Underglazes and such aren't really designated "stoneware" or "porcelain" instead they're labelled by the temperature they commonly fire to. As Neil states, however, many/most underglazes can go to cone 6. The only issue that really has relevance is whether the underglaze color remains strong at the higher temperature.  Many colors fade, as the temperature climbs, so testing is best.

I just looked at the Witgert website. It looks like they make several types of clay for the ceramic world. The fact that your clays are from the same producer, is a good sign, but the fact that they make so many types it will require you to run tests with the actual clays you have. 

[Min]

I developed my porcelain cone 6 slipcasting body then made a plastic version of it for pulling handles. I attached the handles to the cast mugs as soon as the mug bodies were able to be handled (no pun intended). I had pulled and formed the handles and allowed them to dry as much as possible but still be flexible enough to join to the cast bodies. My logic was to minimize the shrinkage difference between the cast body and the pulled handle. Just about every handle still shrank so much more than the body that the handles had serious cracks at the joins. Given that this is just one experience it might not be indicative of what is typical but given that a plastic body is going to shrink more than a non-plastic (casting) body my hunch is it could very well be the norm.

If you were attaching sprigs or other non load bearing attachments then perhaps it has a better chance of working.

[PeterH]

13 hours ago, Min said:

I developed my porcelain cone 6 slipcasting body then made a plastic version of it for pulling handles. I attached the handles to the cast mugs as soon as the mug bodies were able to be handled (no pun intended). I had pulled and formed the handles and allowed them to dry as much as possible but still be flexible enough to join to the cast bodies. My logic was to minimize the shrinkage difference between the cast body and the pulled handle. Just about every handle still shrank so much more than the body that the handles had serious cracks at the joins. Given that this is just one experience it might not be indicative of what is typical but given that a plastic body is going to shrink more than a non-plastic (casting) body my hunch is it could very well be the norm.

If you were attaching sprigs or other non load bearing attachments then perhaps it has a better chance of working.

Valuable experience.

To emphasise the obvious: if @kawaiidumpling wanted to follow this approach they would need to make a casting-slip version of a commercial "sculptural" body. (As you cannot remove the deflocculant from a slip-casting body.)

[Callie Beller Diesel]

On 4/23/2023 at 6:57 AM, kawaiidumpling said:

My local pottery webshop does have both liquid and solid porcelain from the same brand called witgert. But mixing the two is just not very common it seems.

This part stood out to me. Just because they come from the same manufacturer, that doesn’t mean it’s the same clay, or that they’re compatible. They may have similar shrinkage rates, but check to see if they have the same firing range. If it’s not common to mix them, ask why.

If you are excited about slipcasting and incorporating sculpted parts, I would suggest making yourself a flat plaster bat, and pour a layer of casting slip on that to create a slab. You can then use the slab to build hollow parts with, similar to the method Peter linked to. Or there are a LOT of slab building tutorials that could be modified. Look especially for online classes or workshops that mention soft slab techniques, as you will have to work efficiently. Cast slabs can soften quite a bit as you work with them. 

If the casting slip slab is the same thickness as your other slipcast pieces, you can attach them fairly easily. This will work best to create relatively lightweight, hollow pieces.