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Questions about slip casting

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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?

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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

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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

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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.

 

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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?

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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.

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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.)

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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.

 

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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 :)

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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

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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

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