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Repairing cracked ceramics  RSS feed

 
master steward
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Let's explore different ways to fix broken pottery.


I broke my favourite mug a few weeks back.  Beautiful handthrown pottery by my favourite local potter.  All the pieces are there, actually, it's still holding together like a dented egg, but there is no way it will every hold coffee again. Not as it is.  I could repurpose it or use the materials to build something new.  But maybe it's possible to repair it and transform it into a functional mug again?  Or failing that, maybe I can patch it back together and use it for something else.


Kintsugi repair is a Japanese method using lacquer and precious metals.






If we ues gold or silver, the ceramic should be food safe and probably hold water.

Are there other methods for fixing broken pottery?  Pottery is such a wonderful material, easy to make local and far less energy intensive than glass and stainless steel.  Even still, I like to repair things when I can.
 
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There are lots of chemical methods considered food safe by .gov that will stop a leak, but the Japanese method is the best I know. 
 
r ranson
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Can you tell me more about other food safe methods for repairing pottery?  This sounds like a very useful skill to have.
 
R Scott
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Food safe by government standards, not necessarily by mine or yours.

There are a few "food safe" super glues and plain lacquer.  There are also a lot of silicone products for the food industry that are made to seal a crack or seam.  I can't remember the name of the super thin stuff that wicked into cracks so well. 

Red RTV (room temperature vulcanizing) silicone from the auto parts store is supposedly food safe.  Not any other color, just the red.

I am not sure if you really need the gold to make the lacquer work, especially for a crack as opposed to a break.  I need to research this more myself.

I am not a fan of silicone for the fact a re-repair is nearly impossible, you can't get the original silicone out and nothing else will stick to it. 

 
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i started a ceramic midden alongside the trail down to the stream. exhale, toss the broken bits onto the pile and move on.
 
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Thanks for the link R Ranson. I've wondered how they do that for a while - lacquer makes perfect sense. I looked into lacquer a few years ago as a potential finish for my wooden ware, but decided against it because of the allergy issue and complicated curing. A small scale project like this seems like the perfect way to test the lacquer waters.

As to your question: I was always told by my ceramics teachers to use super glue. The regular really liquid kind (not the gel) will get into all those fine cracks. Make sure you don't leave any small crevices where food could get lodged & then go bad. It is food safe, but the repair won't look nearly as nice as gold or silver lacquer.
 
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jennifer piddington wrote:i started a ceramic midden alongside the trail down to the stream. exhale, toss the broken bits onto the pile and move on.



this is me also...we've left a trail of broken handmade pottery behind for forty years...except for the gold/silver repair, I've never seen a 'repair' that satisfied the aesthetics of the piece.  It just always looked glued back together.  I had a 'pot garden' at our last place...spiders, toads, lizards and other crawlies loved it.....
 
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In the back reaches of my memory, there seems to be something about using condensed milk to stick ceramic plates together. Can drag out any more than that right now though.
 
r ranson
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Sourdough starter works really well for glueing together broken pottery.  I don't think it's water safe though, so mostly only for dry goods.
 
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I get this question all the time at my ceramics studio and the answer is always either give up on it or call Sotheby's.  If you're willing to pay 100's of dollars for ceramic repair on the clay level then go for it, otherwise accept the FACT that once broken, a ceramic body will never be healed into as strong and foodsafe a manner as its condition was.
 
r ranson
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David Miller wrote:I get this question all the time at my ceramics studio and the answer is always either give up on it or call Sotheby's.  If you're willing to pay 100's of dollars for ceramic repair on the clay level then go for it, otherwise accept the FACT that once broken, a ceramic body will never be healed into as strong and foodsafe a manner as its condition was.



That's discouraging to hear, but understandable.  I've been doing some reading and talking with potters and the only food safe strong method I've found so far is the traditional Japanese one.

One of the things I learned lately is that clay is a finite resource.  This is what I've heard anyway, and it seems correct.  It's unlikely we will use it up, but still, it makes me think about things differently.  I use to think, oh what's one broken mug, I'll go get another one.  Now I don't want that kind of attitude.  The more I learn about clay and pottery, the more I want to make the effort to preserve what I have - if not as a mug, then as something else beautiful and useful. 
 
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A comment on the posts. 

Super glue works okay for decorative ceramics that don't ever do anything.  The advantages are seams show less, ease of assembly, minimal clamping(usually you can just hold it with your hands) and quick.  Disadvantages biggest is lack of durability if used.  Others include no real gap filling, poor moisture and heat resistance, too quick a set when assembling complicated breaks.  Now one other advantage that no other glue really provides is the wicking type super glue can be use to assemble a piece and then glue it.  Mostly you do you NOT want gels but most other super glues will work.

Epoxy is the most durable of the glue type repairs and is my preferred answer if the object is in use.  Some of the repairs made with epoxy 40 years ago are still in service in lower use items.  Epoxy is messy and seams nearly always show.  In most cases you want a low viscosity epoxy rather than thick to minimize this.  You can get colorants to mix with the epoxy to help hide the glue joints.(works well against solid colored objects especially in primary colors)  Epoxy is messy to work with and no matter how careful you are you almost always end up with glue some where you don't want it.  On the plus side you have good gap filling capability.  All of my long term epoxy experience is from before we worried about food safe.  Now from radiator shop experience know that normal epoxies start to soften about 220 degrees to 260 degrees.  So between that fact and the fact that epoxy like plastic gets hard and brittle over time this is usually what leads to joint failure.

The note about condensed milk is talking about making casein glue.  It is the strongest of the old time glues and is made from milk solids.  You can find hundreds of sets of directions for this glue on google.

Silicone sealant.  I have never used it for pottery but I work with it often in the shop situation and I have to agree with the poster on this.  Poor glue choice and nearly impossible to get rid of if you want to try anything else.  Should be the glue of last resort.   Because of the leverage that pottery pieces apply to the joint this one is virtually guaranteed fail.  Now if it fails getting rid of the silicone in a porous surface is nearly impossible.  If you have to do it best suggestion from shop experience.  Soak the pieces in a high volatility petroleum solvent like gasoline.(48 hours or longer)  The silicone will swell to 4 or 5 times its size and get soft and sort of gummy.  Scrape or peel as much as possible off then scrub the rest hard with an abrasive cleanser or use a sand/soda blaster on it.

Now that covers the ones I know anything about of the posted answers.  2 others I have used.
1.  Plain white school glue.  Not waterproof but easy to apply and okay in the more porous or lower fired ceramics.  High fire and not textured then don't even bother to try this one.  A poor ceramic that the break looks sort of like coarse sand in a decorative object so low stress and this one works fairly well.  Nice thing is easy to get rid of to try again.  Soak in water and scrub hard.

2.  Polyurethane wood glue.  I have one fairly coarse ceramic flower pot glued with this.  Wetted the pieces before gluing to trigger curing.  So far this is working and has been for years.  Don't know how it would work on glassier ceramics.

Now for any gluing of ceramics getting the joint clean is critical to any successful job.  If you just shattered it not a real problem but if it has been cracked for a while.  If most of the break is white but an area is brown with organic cooking type residues is the worst.  Getting that brown area clean is incredibly difficult.  Suggest throwing anything with this away.  It can take many harsh chemicals and hours of labor to clean such an area good enough for glue to begin to stick.  Another hard one to deal with is hard water deposits.  Common in broken flower pots that cracked over time.  Soak in acid like vinegar and scrub repeatedly till you get rid of all you can see.  I have done a couple of these that when the joint broke again it broke right through the hard water deposits.  The glue held but since it didn't stick to the ceramic but instead stuck to the hard water deposit that was what split.  Final wash in any case before gluing should be a residue free spray cleaner to get rid of any oils.

Finally getting glue on surfaces where you don't want it,  Especially epoxy, is common.  A cheap easy way to mask ceramics so the glue can't stick to the surface is to paint the surface with white glue and let it dry.  Then you can soak the glue loose taking the epoxy with it.  Painters paint on mask is another likely good answer here.  Tape is okay for smooth fairly flat surfaces but that is rarely where the break is.
 
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http://hatoya-f.com/simple-kintsugi/for-kintsugi-beginner/


here's a how to for beginners.

please use google translate!
or ask a friend who can 日本語できる!
lol
 
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i've had decent luck lightly taping the pieces together with scotch tape and the boiling the thing in milk for 10-15 mins. Brush milk onto the broken faces first before you tape them together. Let cool and dry and then pry off the tape.

Kept my favorite coffee mug alive this way for years before i finally shattered the thing into too many pieces to be salvageable.
 
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One of the things I learned lately is that clay is a finite resource.  This is what I've heard anyway, and it seems correct.



As I recall from my geology days, clay made into a pot isn't a permanent change (in the geologic scale).  Given a few tens of thousands of years, vitreous (glassy) materials will eventually crystalize and normalize.  I realize given the lifespan of a human, 10,000 years seems damn near permanent, but I derive a little solace in the idea that our pottery will eventually revert, and eventually it may recycle and some vastly distant descendant might reuse it.
 
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