Jump to content
Sign in to follow this  
Polyhedron

Questions about slip casting

Recommended Posts

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: 2s7ZrHX.jpg 

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

Share this post


Link to post
Share on other sites

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

Share this post


Link to post
Share on other sites
29 minutes ago, 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. 

 

lcYLxy1.png

Share this post


Link to post
Share on other sites

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.

 

Share this post


Link to post
Share on other sites
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?

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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.

Krone+modelgips.jpg

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

8023_sib%20ving%20k%20150.jpg

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.)

Share this post


Link to post
Share on other sites

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.

 

Share this post


Link to post
Share on other sites
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 :)

Share this post


Link to post
Share on other sites

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.

image.png.ce3f244e58d6ff9217a180a5156f5043.png

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

 

Edited by Rockhopper

Share this post


Link to post
Share on other sites
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.

image.png.ce3f244e58d6ff9217a180a5156f5043.png

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

Share this post


Link to post
Share on other sites

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?

Edited by Polyhedron

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.