Expert: Sam Kelly - 11/30/2008

Question
QUESTION: You recently answered a question for me on crazing.

I have another.

Apart from me finding the crazing of a piece unacceptable, would you consider the piece unsellable due to it being considered a damaged piece. I asking this as I have sold a lot of work, and today I noticed a piece that I had put aside  for 3 months and then decided to use had a line of  crazing on it, that wasn't there a week ago. So this has obviously taken 3 months to start to craze. (why would it take so long? I'm worried about the items that I have sold to people in the past that may then have crazed months down the track after purches. Am I being too picky or would such an item be deamed unsellable. I have had people say that they don't mind it, adds character, but I'm worried.



ANSWER: Hi Kerry,
Crazing on functional ware is unacceptable, on anything else it's up to the owner/purchaser whether it turns them on or not.

The most probable cause of time taken is the absorption of moisture into the body of the clay.

1- what type of clay are you using, check the specs and see what the absorption percentage is.
2- What is the temp. fired to, has it been fired to maturity.

Functional ware must be fired to stoneware, 1 to 2 percent absorption.

Some earthenware clays have absorption as high as 12%, no good for functional ware.

If you look at the cheap imported pots you will notice very little or virtually none of the pot is unglazed, this is because they are low fired and will absorb moisture.

A hand made pot fired to stoneware(1260degC plus) can have areas of no glaze with no absorption occurring. My coffee mugs are fired to cone 9 with no glaze on the bottom and some of them in the kitchen are 7 odd years old.  

Sam

---------- FOLLOW-UP ----------

QUESTION: Hi,

My work is not functional.

unfortunately I don't fire my own work, or pour the tiles that I cut my pieces from. It's white earthern ware that all I know about it. (I'm buying my own kiln in the next month or so so I can have some control and a better understanding of the whole thing, hopefully.) My pieces are fully glazed with duncan underglazes and I use a Gare glaze.

So am I right to assume that they haven't been fired to maturity??      

Also am I less likely to have these problems with a low fire porcelain? Also would you know if i can use Commercial underglazes such are Duncan on porcelain or do the rich reds burn out as they are of a higher temp???  

Answer
"would you consider the piece unsellable due to it being considered a damaged piece" The answer is YES if you are going to eat out of it or place water in it like a vase etc.

"why would it take so long?" The most probable cause of time taken is the absorption of moisture into the body of the clay. The clay expands over time and this puts stress on the glaze and it cracks, heat will do the same thing.

"Am I being too picky or would such an item be deamed unsellable" again if you are going to eat out of it or place water in it like a vase etc.

"I have had people say that they don't mind it, adds character, but I'm worried." it's up to the owner/purchaser whether it turns them on or not.

If you have sold functional ware(cooking) that has obviously crazed by now then you cannot turn back time, accept that this has happened. Yes it will play with your mind thinking you have sold a product that in time has turned out to be unacceptable in your eyes, but what the hell can you do about it, absolutely zero. Learn from it though, test-test-test and then test again.

If it's only tiles that have been sold then there is no health risk. Set your mind at ease, treat this as a learning curve. Move on, you need  to start making your own glazes and test them on the clay body of choice.

Sam