Questions about slip casting

[Polyhedron]

Hi! I have some questions about slip casting I could not easily find. There seems to be a lot of knowledge here, so I thought maybe someone could help my out with my first attempt in the world of ceramics

1. Is there a minimum draft angle for slip casting? I thought I could easily find this on Google, but I found nothing specific? Does it means that there is none?

2. is it important that the entry where you pour it in is the highest point with slip casting? Very crappy sketch, but something like this:  

Does that curl form a problem when you want to cast it?

[JohnnyK]

Welcome to the forums, Poly...I can't say much about the draft angle, but there will definitely be a problem with the curve trapping air. What you might do is drill a hole at the top of the curve to let the air escape as you fill the mold and when the slip reaches the hole, plug it. Then finish filling the mold.

Others here might have other suggestions from experience. Mine is from a purely mechanical standpoint.

JohnnyK

[Polyhedron]

On 3/12/2019 at 10:21 PM, JohnnyK said:

Welcome to the forums, Poly...I can't say much about the draft angle, but there will definitely be a problem with the curve trapping air. What you might do is drill a hole at the top of the curve to let the air escape as you fill the mold and when the slip reaches the hole, plug it. Then finish filling the mold.

Others here might have other suggestions from experience. Mine is from a purely mechanical standpoint.

JohnnyK

Thanks Johnny!

Here is a better picture of what I want to create. Is there a better way to make this? First I wanted to add the entry to the bottom and manually remove the top of the bowl to open it up, but then I would have a hole at the bottom. 

 

 

[Mark C.]

Think of slip like water and tilt the mold to fill it solid letting all air out. Then as it sits you need to add some slip-this will take so thought to making that mold and having the opening in the right place.

 

[Polyhedron]

19 hours ago, Rockhopper said:

What if you make your mold so it sits on its side ?  Then your pour opening could be in the area that's going to get cut away.

YES! Thanks! I feel so stupid now.

 

16 hours ago, Mark C. said:

Think of slip like water and tilt the mold to fill it solid letting all air out. Then as it sits you need to add some slip-this will take so thought to making that mold and having the opening in the right place.

 

I don't not understand the last sentence, could you elaborate?

[Mark C.]

My point is just as Rockhopper says-you need to fill the mold entirely so make it sit so that happens.

[jakarnes]

If you can find a copy, I suggest grabbing Plaster Mold and Model Making by Charles Chaney and Stanley Skee. It is the most in-depth and technical book about plaster mold making that I have found and it covers draft, undercuts, and their necessity for multiple piece molds in detail. The examples of complex molds and the how and why they were made as shown have been invaluable.

[Polyhedron]

On 3/14/2019 at 1:22 PM, jakarnes said:

If you can find a copy, I suggest grabbing Plaster Mold and Model Making by Charles Chaney and Stanley Skee. It is the most in-depth and technical book about plaster mold making that I have found and it covers draft, undercuts, and their necessity for multiple piece molds in detail. The examples of complex molds and the how and why they were made as shown have been invaluable.

Thanks for the reading tip! I will see if I can find it in my country.

https://krone-gips.de/en/content/products/creative/for-creatives/moulding-plaster.html

http://ceramicbodies.sibelco.eu/sites/default/files/datasheets/en/K150_en.pdf

Can somebody verify that these are compatible for slib casting? Especially the plaster for the mould. (I would like to check if I made any translation errors from the English tutorials I looked up.)

[Polyhedron]

1 hour ago, Rockhopper said:

Looks like your plaster is what is known in the US as 'Plaster of Paris' or 'Casting Plaster'.  The "moulding shapes and figures" on the label refers to pouring the plaster into a mould (usually rubber or alginate) to make figures, that are then painted.  It tends to be somewhat soft and easily damaged - especially when it gets wet - so probably not a good choice for slip-cast moulds that you want to use more than once or twice.

Look for something called 'Pottery Plaster' (for example: https://www.saintgobainformula.com/product/pottery-plaster), that's formulated specifically for the purpose.

 

Thanks, you just saved me for ordering it!

I am trying to find it in The Netherlands, but I have a hard time finding it. I will try to email some shops. If there are fellow Dutch people reading this, please let me know if you have a link/keyword 

[Polyhedron]

22 hours ago, Rockhopper said:

The company I linked to (Saint Gobain) is a very large, international company.  Their website displays contact info  based on the country you select...  When I selected 'Netherlands', it shows 'Patrick Lesch' - with an email address and phone number.  I would suggest sending him an email and ask if there is a distributor in your area.

PS - I have no connection with this company - just selected them as an example because I know they are a European based supplier.

 

Thanks for the tip! I also found this link when I reached out to the owner of  webshop. I thought I post it here if someone Google this page in the future:

https://www.keramikos.nl/vormmaterialen/961-gips-vigo-albast-25-kg.html?search_query=vigo&results=2

[Polyhedron]

Just made the model and cottle boards. I had some questions regarding the next steps.

1. I used a 3D print combined with clay. If I want to make a mold I need to hover so I make the first half of the mold like this:

Can I use a release agent so the clay won't stick to the hardend clay?

2. Can I use dish washer soap with water as a release agent for question 1?

3. Do I need to wait for the clay to cure (before I pour the plaster)?

4. He uses a wooden board for a divider. Can I just use the clay and flatten it?

5. Can I use dish washer soap with water as a release agent on the mold when I am going to slip cast it?

[Bigbellceramics]

Polyhedron- I’ve self taught myself slip casting over the past month and have learned the hard way that you MUST have a wooden or steel divider. The last thing that you want after all the effort that you’ve put in meticulous preparing your piece to be molded is watching your plaster pour on the ground once immediately breaking through your divider. It will ruin your day and make a big mess for you to clean up. Your divider has to basically be air tight so no plaster will leak through. Close up alol corners with clay to seal your frame. Well worth the preparation!

 

Although unadvised, i used normal dish washer soap as a release agent but I brushed on multiple layers to make sure my object wouldn’t get stuck.

 

Finally, make sure that your plaster is properly mixed or it will not dry and you will be left with yet again, another big mess.

[neilestrick]

Liquid soap will work as a release agent during the mold making process You may need to add just a little water to it, depending on how thick it is. Be sure to brush very slowly when applying it, so you don't create bubbles. After the plaster mold is done, wash it well to remove any soap, then let it dry completely before using it. Depending on the thickness of your mold and the humidity in your environment, it may take a week or two for it to dry completely.

[Chilly]

On 3/30/2019 at 10:00 PM, Polyhedron said:

Just made the model and cottle boards. I had some questions regarding the next steps.

1. I used a 3D print combined with clay. If I want to make a mold I need to hover so I make the first half of the mold like this:Can I use a release agent so the clay won't stick to the hardend clay?

2. Can I use dish washer soap with water as a release agent for question 1?

3. Do I need to wait for the clay to cure (before I pour the plaster)?

4. He uses a wooden board for a divider. Can I just use the clay and flatten it?

5. Can I use dish washer soap with water as a release agent on the mold when I am going to slip cast it?

Haven't watched the video, but here are some answers for you:

 

5.   NO, absolutely not.  Make sure any soap used during making the mould is thoroughly removed, using vinegar.  Then dry for several days in sunshine/breeze/fan.

1.  Not sure I understand the question.

2.  Possibly, but if you can, get hold of soapy release.  Much thicker than dishwash.

3.  No, you can pour plaster onto wet clay.  In fact if you wait for the clay to dry, it will shrink and change shape.

4.  Not sure of the context, but say I was making a mug mold from a commercial mug, I would bury half the mug in damp clay, burying half the handle.  I would then run a bead of clay up the inside and outside of the cottle boards, making the inside ones nice and rounded and smooth.  This will give my finished mould a rounded edge.  The outside is to make sure the plaster doesn't leak.  (Also, if using a commercial mul, I would fill the inside with clay, making a funnel shape to give me a pouring reservoir.)

Hope that helps

 

[Kerryanne Foley]

I would like to slip cast a found object a teapot. Do I paint teapot in a soft soap before I place into plaster. Can I make a mould this way as when I see reference information they make the mould from clay I don't want to do this can you assist with this. Also U have liquid soft soap used for ceramic I have dispex do I put this in the plaster mix and I have liquid wax do I put this in plaster mould before pouring in slip.

Thanks Kerryanne

[PeterH]

On 3/17/2019 at 4:43 PM, Polyhedron said:

Thanks for the reading tip! I will see if I can find it in my country.

>Plaster Mold and Model Making by Charles Chaney and Stanley Skee

Great book, although even 2nd hand copies are getting pricey.

If you have trouble finding a copy then  Amazon offer it, and will probably post to your country.

I usually search via bookfinder.com
With destination UK and currency £ I get https://www.bookfinder.com/search/?full=on&ac=sl&st=sl&ref=bf_s2_a1_t1_1&qi=FJ3u2dxYsA9KydVvBwBkn0IEfQM_1497963026_1:1:3
You might try modifying the search to your own country and currency.
 

[Polyhedron]

Hi everyone, small update on the side project. I want to thank everyone in this topic! I learned a lot and if it wasn't for a few tips I never figured it out and probably would have quit it (especially the tip about the orientation of the mold). It wont be my last ceramic project (although I need to be more calm when I accidently break stuff.. )