Jump to content
Sign in to follow this  
Roberta12

How to tell if unmarked clay is high fire or mid fire

Recommended Posts

Roberta:

start with color: terra cotta is obvious, but not to be confused with red stoneware. Earthenware is easy to spot by its nearly white color. 

Did this potter mostly use porcelain or stoneware?  Porcelain can run off white to,light tan: pending type and plasticizer used. On occasion ball clay is used, which turns porcelain a tan to med. gray. Stoneware can run tannish to brown pending ball and fire clay % and type. If you have thrown porcelain and stoneware on the wheel; will also give some indication. Can you feel any type of grog, sand, or grit? Another indication: typically only stoneware uses grog. Almost all porcelain and stoneware are cone 6 and up? What were the cone ratings of the kilns used by this potter? Another indication.

Make a six by six tile: then do the standard absorption test. I would start at cone 8 and check it. Absorption testing will tell you the vitrification level, which in turn determines cone range.

T

Share this post


Link to post
Share on other sites

You are lucky it is just one clay,  I had a friend from college get out of the pottery business.   She called and wanted to know if I wanted her clay,   I said sure and thought we would talk about it another day.   A few days later I found a dozen 5 gal buckets on my driveway,  dried up and no marking on the buckets.   The clay in the buckets were different colors also,  my husband and I decided it wasn't worth rejuvenating and testing them.   We were lucky we had a small creek behind our house that the city was diverting and filling in,  we dumped the clay into the old creek.   Denice

Share this post


Link to post
Share on other sites

I don't fire to cone 10, but I know some friends that do.  And I like the absorption test idea also.  I really hate to just pitch all this clay.  There is a big barrel of rock hard, really white clay.  My assumption is that it is porcelain.  I think he used both.  But there is an old refrigerator full of a medium brown clay.  Most of it still soft.  I think he fired gas in the past, but in more recent years he must have been firing electric.  A family member took the kiln that was in the shop.  I did not get to see it.  I have seen no evidence whatsoever of earthenware.  

Thanks friends for a direction!

Roberta

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×

Important Information

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