China Figurines Cracking - What Reason Could This Be?

by Philip
(Canada)

China Figurines Cracking - What Reason Could This Be?:- I do porcelain restoration so I guess I approach the subject from a different point of view but I do have a question that I think would interest many of your collectors. I have had at least four figurines and one piece of flatware that have developed cracks.

These cracks open up over time and sometimes the piece is found literally broken in half with no contact being possible. I have one figurine under observation and the crack is now about 3mm wide at its widest and growing. I'm at a loss to explain this to clients and it is particularly frustrating that only one figurine in a display is effected.

Whatever causes this must be long delayed too because sometimes the piece is over fifty years old and is only now developing cracks. I'm suspicious that storing in a humid place is somehow involved but why does this effect only a few pieces. I'm wondering if it is caused by a combination of causes. Your comments?

Philip

==============================================

Reply by Tony (admin)

to China Figurines Cracking - What Reason Could This Be?

Dear Philip,

I was forwarded your query regarding porcelain cracking and I have a theory as to what may be causing it.

I think that it is to do with the 'fit' of the glaze to the body of the porcelain.

When I was at college making ceramics, back in the mists of time, I remember that we had a particular problem with 'fit'. It is technically to the co-efficient of expansion of the glaze to the body clay.

This means that the body and the glaze need to be formulated to expand and shrink due to variances in temperature and moisture at exactly the same rate. Modern ceramic companies such as Wedgwood have spent a lot of money and time to get this right. My college ceramics were not quite so well advanced technically and there were numerous occasions where fired pieces cracked or even split in two. I remember making a batch of teapots for friends, one time and they all cracked when hot water was put into them - not the best way to impress people!

The teapot example shows the dramatic effect of a sudden change in temperature.

A piece such as a figurine will not normally undergo such treatment but over time it will happen if the 'fit' is not right. The slight cracking and crazing of glaze is called 'pinging'. We used to hear the high pitched 'ping' a lot at college. I remember seeing pieces newly out of the kiln still cooling down, that pinged like crazy - bits of glaze sometimes used to crack off.

If the fit is nor right there is nothing that you can do to stop it.

Imaging a fat person really squeezed into a tight jacket - eventually the buttons are going to pop off - something has to give!

If the fit is not too bad, a piece can last years, maybe pinging every so often, and then there is the final change (maybe just from summer to winter) that finally gets it.

It does happen to top firms such as Wedgwood every once in a while when something goes wrong with a new batch of ingredients, but it is very rare. The older a piece, the more likely that the formulas for glaze and body are not quite matched because of the technology and knowledge at the time. It is why old pieces show crazing.

I hope that this helps even if I do not have the solution once the effect had happened.

best regards

Tony

============================================

Further Comment by Phil

To China Figurines Cracking - What Reason Could This Be?

Dear Tony,

Thank you very much for this detailed reply. I am a retired mechanical engineer so I understand your explanation completely.

Actually it ties in totally with our climate (Canada) and in particular with a Coalport cake stand and a platter that I repaired recently. I know the history of these two a little. I usually don't know much about pieces I repair but sometimes I do.

The Coalport had been stored in a loft and here in Canada lofts are very cold in winter (-30ºC) and can get very hot in summer (+50ºC). This is because all the house insulation is in the ceiling and the loft itself is vented.

In summer the sun shines on the roof and elevates the inside temperature of the loft well above ambient despite the venting. That is a guaranteed temperature swing of 80ºC !! And every year!

I have no idea how many years, but a lot. It is probably a tribute to Coalport that it even stayed together!

The other piece I know the history of is actually on my website, www.philipsporcelainrepair.com it is a Dutch family heirloom and crossed the Atlantic three times.

It had broken twice and although I don't know the history of the first break I do know the history of the second one. It was wrapped in a heavy table cloth and buried in a suitcase in Holland and then accompanied the owner back to Canada. When the suitcase was opened the
platter was in pieces. Now I do know that aircraft luggage compartments are not heated and the temperature can drop to extremely low temperatures (like -50ºC).

The owner blamed the baggage handlers but it seems entirely likely that the break was caused by temperature change. If you check it out on my website you will note that the break was multiple. The material was
primitive having been made locally in Holland shortly after WWI so a temperature stress situation would be extremely likely.

I think Peter could make an interesting and informative article in his newsletter about taking figurines into the passenger cabin rather than putting then in luggage when flying. I know that I will be doing that from here on in!

I am fairly new to the world of porcelain, well OK I still have my collection of crest-ware, which I started collecting when only ten, but I find the repair fascinating and only wish I had got into this years ago.

It is sure a lot lighter work than steel fabrication and construction but in other ways remarkably similar.

Thanks again to both of you, I will be passing this information along to MacIntosh China in Kingston who refer clients to me and have asked about cracking themselves.

I'm so glad I took the time to contact you.

My commiserations about the teapots but it makes a good story.

All of the very best,

Philip