Friday, May 31, 2013

Crazing

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Mickey's Glove/Hand Shows Signs of Crazing
Over the years, I have had many collectors email regarding crazing. Fortunately, I've never had it happen to one of my own.

I recently purchased Fishing Mickey from The Simple Things. At first glance, didn't even notice any signs of it. It wasn't until I began to photograph the sculpt that I could see crazing had begun on Mickey's hands/gloves.

What is Crazing? Crazing is the fine crackling one often sees on many fired porcelain pieces. Crazing is in the glaze and is not detectable when one rubs his or her fingernail over the crazing. Crazing occurs during production when the clay body and glaze cool at different rates. Crazing is a very common condition with virtually all glazed porcelain. Normal crazing or crackling that cannot be seen at a few feet does not typically affect the value of most very high quality art pottery pieces. Buyers should expect some crazing on all glazed or hand-painted art pottery.

Because the clay and glaze of a piece have different chemical compositions, they respond differently when heated in the fire or a kiln. Both clay and glaze will expand under heat, but they do so at different rates.  They also contract when cooled, again, at different rates. If the rates of contraction are too different, and the glaze contracts more than the clay, the glaze will crack under tension.

Most crazing occurs after the final firing of a piece, when the piece has cooled. Some crazing occurs at other times, during thermal stress or if the pottery is left exposed to extremely cold weather.

'Crazing' or 'craze lines' are not cracks. Crazing effects only the shiny glaze on the porcelain, leaving it with a cracked appearance or what looks like tiny lines running in random directions. Age and temperature conditions can cause crazing to occur in various degrees. It typically does not detract much from the value of a piece unless it has become stained beyond what the buyer considers appropriate or the crazing is so severe that it over shadows the beauty of the piece.  Normal crazing is usually an acceptable characteristic found in older porcelain.

This is the one disadvantage of buying a piece through eBay vs. an Authorized Dealer as you don't know how a piece was stored and can't always go by photos. Thankfully not too noticeable and hopefully won't get any worse.

2 comments:

Timon said...

Great post, Don. It's a good explanation for those who are unfamiliar to crazing, and a reminder to those who know about it.

Of course I have several pieces in my collection that have crazing, and like you said, it's a common occurrence. You just have to look past it.

From a distance you don't notice it, but of course I always know it's there. I think it's more visible with the pieces that have white, like Mickey's gloves. But my Fantasia Diana piece, which is a light blue, has signs of it as well.

Some of the pieces, like Diana, are so beautiful, I don't mind the crazing. I'd rather have the piece with crazing than not at all.

Duckman said...

Thanks Tim! Can't tell you how many times I've been asked about crazing, nice to have a good reference associated with the website on it.

Like you, my eye keeps going to it but it doesn't distract at all from the artistry of this piece.

From emails, it seems the crazing is most apparent in the white and flesh tones coloring. Your Diana is the 1st I've heard in the opalescent paints.

Once the crazing began, did it continue, get much worse or do its thing and then done?