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Callie Beller Diesel

Quick question about extra large bowls.

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I have a commission for a larger bowl than I usually make. Just to save time, can people who make a bowl that’s about 16” finished diameter  tell me how much clay you start with? The overall form needs to be a bread bowl style: rounder aspect as opposed to a more upright style, but not too shallow either.

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That's a really difficult skill, judging how much clay to make a specific size and shape that's not a frequently repeated product.  I can somewhat do it after 25 years.

I don't think it's anything that can be taught or even calculated.  Human brain is really marvelous. 

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I make sinks that are 16" in diameter, but I leave them thicker than a regular bowl, and I do them in porcelain which has a higher shrinkage rate, but I use 18 pounds for those. So Liam's 12 pounds is probably a good starting point. Or go with 14 pounds and cut off the rim if it gets too big.

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On 7/30/2020 at 4:45 PM, Callie Beller Diesel said:

I have a commission for a larger bowl than I usually make. Just to save time, can people who make a bowl that’s about 16” finished diameter  tell me how much clay you start with? The overall form needs to be a bread bowl style: rounder aspect as opposed to a more upright style, but not too shallow either.

Callie,

This worked for me when I was required to make large punch bowls.

early on, I quit using weight of clay for estimating clay requirements, and switched to volume.  Easy to estimate and to measure.  Set my units to be cm or 10's of cm.  
Sketched the profile of the bowl showing the outside and inside surfaces in a cross section assuming that the bowl was half of a sphere.
wrote down the dimensions of the diameters and wall thickness targeted.  
Assumed that the shrinkage was about 15% wet to final. so the dimensions were 15% more than my target dimension.
got out my geometry formula tables and my slide rule and made some volume estimates of the cc's of clay needed.   
added some volume to allow for the foot ring.  
rounded that up numbers to even 10CC  and took the cube root of that volume to be the size of a cube of wet clay.  

LT 

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