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Expiration date


Gabby
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Do underglazes and glazes have any sort of expiration date?

Specifically, I have some little containers of underglaze I bought perhaps three years ago that I have not used since. I now have something on my workbench I want to decorate with more than my common black, white, green, or blue and so opened up some of those old colors to find they look like the desert in the dry season.

Can I simply reconstitute them with water, stir well, and use, or has something changed due to my lack of attention to them that makes them unusable?

They have been indoors.

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You can reconstitute them with a little water. It involves a lot of stirring to get the lumps out because of the gum and other binders in the underglaze that make them paintable, but they’re rescueable. 

Add the water a little bit at a time so they don’t wind up too runny. 

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Commercial glazes won't go bad in the sense that they aren't usable, but their brushability can go bad. Because the gums that are used to make them brushable are organic, they can get eaten up by bacteria over time. If that happens you'll know it as soon as you try to brush on the glaze- it won't flow, and will dry almost immediately, making it impossible to brush an even coat. If this happens, there are commercially available brushing additives, or you can make your own from CMC gum.

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18 minutes ago, neilestrick said:

Commercial glazes won't go bad in the sense that they aren't usable, but their brushability can go bad. Because the gums that are used to make them brushable are organic, they can get eaten up by bacteria over time. If that happens you'll know it as soon as you try to brush on the glaze- it won't flow, and will dry almost immediately, making it impossible to brush an even coat. If this happens, there are commercially available brushing additives, or you can make your own from CMC gum.

Thank you.  These old ones are whatever the tiniest size is of commercial underglaze, so if it takes more than adding water gradually and stirring well, I would probably just toss them and replace. There are only about five of these.

Does what you have described happen to glazes as well- that they lose brushability because of bacteria? I use only brush on glazes.

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1 minute ago, Gabby said:

Thank you.  These old ones are whatever the tiniest size is of commercial underglaze, so if it takes more than adding water gradually and stirring well, I would probably just toss them and replace. There are only about five of these.

Does what you have described happen to glazes as well- that they lose brushability because of bacteria? I use only brush on glazes.

Yes, to any glaze product that you buy in wet form, intended for brushing. But it takes a long time sitting on a shelf for it to happen.

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When re-slurrying previously suspended solids in the research lab, it was standard operation procedure to first crush/grind the solids in a porcelain mortar and pestle (MP) and sieve out the fines, and grind the solids to a very "fine" powder.  Then the powder was wetted and re-suspended. 

I have made my own MP from porcelain.  Just create a  small thick wall bowl with a rounded interior bottom and a rounded bottom club. fire the parts unglazed to the clay maturity temperature with a long hold.  Unless you are trying to crush diamonds it works OK for breaking up "lumps" into "fines" I oftenly used a tightly stretched piece of silk as a sieve for fine powders. 

LT

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17 hours ago, Magnolia Mud Research said:


When re-slurrying previously suspended solids in the research lab, it was standard operation procedure to first crush/grind the solids in a porcelain mortar and pestle (MP) and sieve out the fines, and grind the solids to a very "fine" powder.  Then the powder was wetted and re-suspended. 

I have made my own MP from porcelain.  Just create a  small thick wall bowl with a rounded interior bottom and a rounded bottom club. fire the parts unglazed to the clay maturity temperature with a long hold.  Unless you are trying to crush diamonds it works OK for breaking up "lumps" into "fines" I oftenly used a tightly stretched piece of silk as a sieve for fine powders. 

LT

What a useful tip.  I will try it.

 

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The jars are probably 2 oz. I got a bunch of them from a friend and they were all dried out, I did what LT suggested and reconstituted them and haven't had a problem. Most of them were half full and colors that I would not normally use but they were fun to play around with on miscellaneous pieces like cat food bowls, spoon rests, pinch pots, etc.

JohnnyK

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Nope never.....I have glazes that where created in the 1960's.  Just thin with water but if they are solid rock, remove as much as possible from the jar.  Break apart into smaller pieces. I use an old fork or butter knife and the lid from a cookie tin to contain the pieces. Put back in the jar, add a bit of water and shake. If its too thin, leave the lid off to dry out. and thicken up

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10 hours ago, preeta said:

Well. If one talks of functional ware... in a way yes... like paint ... depending on how old.  

Lead

barium

lithium

 

What I am doing this week is not functional ware, but are you saying things with these elements expire in the sense of spoilage or only that we no longer use paints/underglazes with these ingredients whereas they were used years back?

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I've had unopened/ sealed bottles of commercial glaze, change consistency before using.  It's usually specific glazes, and I have to fight them quite a bit, to make them usable again.  I've been meaning to email the company, but haven't gotten around to it yet...

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3 hours ago, Gabby said:

What I am doing this week is not functional ware, but are you saying things with these elements expire in the sense of spoilage or only that we no longer use paints/underglazes with these ingredients whereas they were used years back?

the presence of ingredients.

i feel like oil paints glazes dont spoil as in lettuce. they cure/change depending on chemistry. here we come across old stuff in garage sales all the time. many years old.  one immediately wonders about 'spoilage, but its more about what ingredients are in it. 

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  • 1 year later...

So in regards to expiration date. I have gained access to our kiln room and it is fully supplied with paints, glazes, under glazes of all types. But the room has not been utilized in 10 or so years. Most of the supplies has either not been opened or was only used for a short while. I don't know if we have the budget to get everything brand new (will probably take some fundraising) but can any tell me how to approach this. Most supplies are either Duncan Bisque or Mayco. Thank you in advance :)

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Hi @Ariana

I took on an after-school pottery class in a primary school several years ago.  We had to buy clay, but there were jars of glaze that hadn't been touched in many years.  Some worked fine, straight out of the bottle, some needed a little attention, some I never got into a useable state.

The only way is to test.  Some glazes settle so hard, it's really hard work, and in terms of hours spent, it's probably cheaper to spend £20 on a jar of glaze than 2 hours trying to get it workable.  Depends on whether you are time-rich or cash-rich!

One tip that I saw (think it was John Britt) is to use a tool like this image.png.138c6b2afb0710450b72b5247d0232b5.png to scrape the dried hard glaze into fragments/dust (wear a dust mask) before re-hydrating.  If you can get the tool into the jar of course.  And yes, I've cut many a plastic bottle in half to get at the glaze inside.

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@Ariana, sometimes the gums in brushing glazes deteriorate over time. I'ld suggest getting them mixed up like Chilly suggested then trying them on a scrap of bisque. If you find they don't brush well then add some gum solution. You can mix your own or use a premade one like this one from Amaco.  The other ingredients in the glaze will still be fine, the minerals that make up the glaze won't expire. 

A blender will quickly mix everything up, then pour the glaze through a sieve (80 mesh would be fine).

Edited by Min
added a thought
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19 hours ago, Ariana said:

Most supplies are either Duncan Bisque or Mayco.

Whether they can be successfully re-constituted will vary with type of product, and whether they've just thickened and/or separated - or are completely dried out. 

Glazes, and under-glazes can probably be salvaged - but I think you'll find that your "Duncan Bisque"  is actually an acrylic paint ("Duncan Bisque-Stain"), that is applied after all firing is done.   If these have thickened, but are sill moist, you can probably add a little water and stir - but if they're bone-dry, they're likely destined for the trash can. 

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Hi Andy!

Looks like your antique materials are in great shape! ...however, lead (and a few other materials used in ceramics) are viewed differently now vs. then; proceed with utmost caution would be my advice.

https://digitalfire.com/4sight/glossary/glossary_lead_in_ceramic_glazes.html

"...the CDC has now published its statement that there is no level of lead that is "safe", and it has lowered its "reference" level which it wants people to get upset about if they discover their children testing higher than to a fraction of what it was when we were children. Lead is so widespread that reducing human exposure to anything close to pre industrial levels may not be economically feasible, especially given all the other problems civilization is faced with, however, all authorities are setting policy to encourage people to reduce whatever chances of exposure they are causing, then to reduce that again."

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@Splodgeink, as well as the chance of lead as @Hulk pointed out I would be extremely concerned that uranium oxide will probably be in the orange and reds. It's just not worth taking the chance with these, I would suggest handling them as little as possible and getting them disposed of through a toxic waste facility. 

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Looks like the Wenger company and Mason both started out in Stoke on Trent but I don't think the colour name Victoria Green is proprietary to Mason. I found this little bit below about the name of that colour (from this link).

"Origin and History

The origin of this pigment is obscure. The potter Sir William Burton introduced the pigment to the Society of Mural Decorator and Painters in Tempera in about 1900. The Society of Tempera Painters named the ceramic pigment Vernalis. Victoria green was the name designating a calcium chromium silicate pigment developed for use in ceramics. The name was also used by artists' paint manufacturers to designate a mixture of 80 parts of Viridian (Pigment Green 18), 40 parts of zinc yellow, and 10 parts of barite, gypsum, lithopone or zinc oxide (Pigment White 4). Victoria green was sometimes called permanent green. The Colour Index lists a green oxalate dye named Victoria green as Basic Green 4 (42000)."

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