I believe the testing was done and published in Ceramics Monthly. If I get
bored, I will send them an email to check. They do answer them.
The commerical mixtures are supposed to be good.
I have not used them.
I did try the vinegar. It did not work for me, alas.
Could be the type of clay body you have that does not shrink as much as
mine. Vinegar is 99% water isn't it? I am not a chemist. Can you tell?