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Hi everyone,

 

A question. Can anyone see a problem with not glazing over underglaze for non food works?

 

I have looked but can't find an answer anywhere and it seems that everyone uses a glaze over the top for the underglazes. I'm using porcelain clay to make wearable works including rings (I should add). I love the results, and the undergalzes adhere very well to the porcelain. I can even wet sand after the final fire and the design stays put. The colours appear somewhat softer but that is good too. I belive that the newer underglazes have more frit in them making them a litle more like a glaze themselves and this is why they work differntly to older style glazes.?

 

Any issues? I can do it but is it a bad idea as far as safely goes?

 

cheers

 

Lilly aka etched

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I'm not sure what temp you're firing the final time but I hope this helps:

My sister uses Duncan underglazes extensively in low fire work and my potter friend used to use them extensively in higher fire work (she has switched to all Cone 5 glazes now). At Cone 05, about 1/3 of the glazes complete to a beautiful gloss, and the other 2/3 do not complete but range from a grainy matte to a streaky satin finish without clear over them, quite unpleasant. You have to do samples and see which ones those are. At Cone 5, all underglazes complete without any clear coat, but certain colors have a tendency to run and bubble if they are being applied to bisque for the first time though they're fine if applied to green ware. Occasionally they will pit when applied to non-bisque ware. I've been using Duncan's green underglaze on some of my sgraffito work and it's been fantastic with or without a clear coat over it. Zero problems, no bubbling, no running. You still want to test everything because the colors change at different temperatures, of course.

 

Mayco underglazes complete at Cone 05 to a gloss. I think they're called Stroke and Coat and I'm 99% sure they're all food safe, as are all the Duncan underglazes. 

 

If you do clear coat over underglaze I highly recommend allowing the underglaze to dry thoroughly before application of clear. I ended up learning my lesson on that with streaky work. :( No bueno.

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I use underglaze (usually black) on non-food surfaces without a clear or other glaze. I also may use a wash (rutile). I do apply a soda ash wash so give the bare clay a bit of a sheen (1/4 cup soda ash dissolved in 1 cup hot water, applied with a sponge). Fire cone 6 oxidation.

 

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post-2190-0-84350100-1438597717_thumb.jpg

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Amaco Velvets are made to be used with or without a glaze cover. The only issue I would see is the oils from the skin being absorbed and eventually dis coloring the piece. I think you could then probably just wash it in soapy water but have not tried so not sure. I have a bracelet a friend made and it is unglazed and since the clay was fired to maturity, it is just fine after years of wear.

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It is probably a good idea not to have the underglaze in contact with the skin. Could make it part of the design to have inside raw porcelain just to be safe but I don't know how unsafe it is in reality.

 

If the underglaze doesn't stick to the shelf no problem using it.

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thankyou for all your replies!

 

Im in Australia so I dont think we can get the Amaco underglazes... but I'm using Chransanthos one stroke underglaze only the black.

 

Im firing to cone 9 (1280 degrees Celsius) on porcelain.

 

Great idea in regards to contacting the manufactures, I didnt think of that for some reason...

 

I supose a lot of people use underglazes with low fire clay where you have to glaze so maybe thats why I found it hard to find anything on unglazed underglazes?....

 

cheers Lilly aka etched

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I can't see it being a health issue in the minute quantities that you'd have next to your skin. You did mention that once you sanded the pieces after the final firing and the colours got softer. For most of the jewelry that's probably fine too, but for rings that are going to be exposed to more daily wear on a hand does this present a problem long term?

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just looking at some Amaco underglazes.

 

LUG series or Lead Free Underglaze the manufacturer recommends an LG ,F or HF glaze over it to make the piece dinnerwear safe.

V series or Lead Free Velvet Glazes the manufacturer recommends covering with LG, F,LM, DC, or HF  glaze over it to make the piece dinnerwear safe.

 

While they may not contain any LEAD there are probably some heavier metals used in some of the colors which is my guess as why they are recommending this.  The other possibility could be increase the wear ability especially if someone is going to run the pieces through a dishwasher repeatedly.

 

My question though is if it truly an underglaze if it contains any frit at all?  The frit can make the "underglaze" flow  as well as create an none velvet surface.  

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I think they recommend using glaze over it to seal the surface for the usual sanitation reasons. Most people want to know what glaze the manufacturer has matched the product to.

I have used underglazes for years and on outdoor sculptures that are not totally glazed ... they still have their colors after many years exposed to the elements.

Unless I am totally misreading the product safety sheets, there are no dangerous metals.

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My question though is if it truly an underglaze if it contains any frit at all?  The frit can make the "underglaze" flow  as well as create an none velvet surface.

To work at low fire temperatures, you need either a frit or borax or gerstley borate to help melt the underglaze and adhere to the clay body. Without the frit, etc., the underglaze may not melt enough and brush off after firing. If you apply your underglaze at greenware stage, that frit is really good to adhere the underglaze to the ware; then, you can add glaze over. So, yes, it is an underglaze even if it has frit or other melting addition.

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I think they recommend using glaze over it to seal the surface for the usual sanitation reasons. Most people want to know what glaze the manufacturer has matched the product to.

I have used underglazes for years and on outdoor sculptures that are not totally glazed ... they still have their colors after many years exposed to the elements.

Unless I am totally misreading the product safety sheets, there are no dangerous metals.

 

Hard to tell, it seems to lump everything together into 'Inorganic Stains, Carbonates or Metal Oxides' and talk about dangers when using the product, nothing to do with after the firing. 

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 You did mention that once you sanded the pieces after the final firing and the colours got softer. For most of the jewelry that's probably fine too, but for rings that are going to be exposed to more daily wear on a hand does this present a problem long term?

Not sure what gave you that impression Disel Clay but I said I can even wet sand the work at the end and the colour stays put:) So I'm superconfident that theer will be no rub off at all. Only chipping will be an issue but I have read that work that isnt glazed is actually less likley to break, not sure what is the reasoning behind this though,

but interesting!

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Hi everyone just contacted the manufacturer and thought that I would include his response in case anyone is interested.

 

 

I think that if you are firing to 1280 and its glossing up, there should not be any problem. But it must gloss up. If it doesn’t, you need to use a clear glaze on top...

 

If the surface is smooth like say a satin glaze finish… it will be OK… If it has very small holes in it, then glaze it.

 

The glaze will stop any nasties from leaching out into food or drink. Nasties are things in the stain that it is made from. Not lead, but things like Cobalt.. The quanties that leach out are so small they would be undetectable and may never cause any problems… but its better not to get that exposure if not necessary.

 

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Hi everyone just contacted the manufacturer and thought that I would include his response in case anyone is interested.

 

 

I think that if you are firing to 1280 and its glossing up, there should not be any problem. But it must gloss up. If it doesn’t, you need to use a clear glaze on top...

 

If the surface is smooth like say a satin glaze finish… it will be OK… If it has very small holes in it, then glaze it.

 

The glaze will stop any nasties from leaching out into food or drink. Nasties are things in the stain that it is made from. Not lead, but things like Cobalt.. The quanties that leach out are so small they would be undetectable and may never cause any problems… but its better not to get that exposure if not necessary.

 

Can I ask which manufacturer you contacted.  The reason I ask is that are numerous producers of under-glazes as well as different underglazes from some of the manufacturers.  An example is Maco, Duncun, Amaco, and Laguana to just mention a few.  I'm sure each of these manufacturers use there own formulas so what might be safe from one manufacturer might not be as safe from another without an over glaze.  Perhaps even some colors by a said manufacturer may be safer than other colors from the same manufacturer.

 

Then there are some glazes like Anaco ST-23 Light Blue that are listed as none food safe do to there open pores which can cause bacteria issues.  Which make me wonder if the open pores on some of the underglazes are the reason they recomend a top glaze on rather than just the chemical makeup?

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My guess is all the underglaze manufacturers are going to recommend a clear glaze over their products if used on a wares intended for food/drink. The clear glaze helps protect against leaching. Some of the stains used in underglazes -- especially reds, some yellows -- use cadmium and are encapsulated to prevent leaching. And, my guess is the manufacturer's claim for being food safe is based on their underglaze with their clear glaze fired with their firing program in their kiln. Your clear may have a different chemical composition. The only way to truly know if your clear over their underglaze in your kiln is non-leaching is to have an item tested by a laboratory. If the underglaze uses cadmium (and the various color charts list that info), then that is what you test for.

 

The original post asked about underglaze without a glaze covering on non-food surfaces/items, like jewelry. Some people may have a reaction to certain chemicals/materials (I remember a problem with pierced earrings using copper hoops/pins and piercings turning green). But I am not sure you can test for every possible situation.

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Hi everyone just contacted the manufacturer and thought that I would include his response in case anyone is interested.

 

 

I think that if you are firing to 1280 and its glossing up, there should not be any problem. But it must gloss up. If it doesn’t, you need to use a clear glaze on top...

 

If the surface is smooth like say a satin glaze finish… it will be OK… If it has very small holes in it, then glaze it.

 

The glaze will stop any nasties from leaching out into food or drink. Nasties are things in the stain that it is made from. Not lead, but things like Cobalt.. The quanties that leach out are so small they would be undetectable and may never cause any problems… but its better not to get that exposure if not necessary.

 

 

Can I ask which manufacturer you contacted.  The reason I ask is that are numerous producers of under-glazes as well as different underglazes from some of the manufacturers.  An example is Maco, Duncun, Amaco, and Laguana to just mention a few.  I'm sure each of these manufacturers use there own formulas so what might be safe from one manufacturer might not be as safe from another without an over glaze.  Perhaps even some colors by a said manufacturer may be safer than other colors from the same manufacturer.

Then there are some glazes like Anaco ST-23 Light Blue that are listed as none food safe do to there open pores which can cause bacteria issues.  Which make me wonder if the open pores on some of the underglazes are the reason they recomend a top glaze on rather than just the chemical makeup?

thankyou for all your replies!

Im in Australia so I dont think we can get the Amaco underglazes... but I'm using Chransanthos one stroke underglaze only the black.

Im firing to cone 9 (1280 degrees Celsius) on porcelain.

cheers Lilly aka etched

Also I'm not after food safe just safe for skin contact:)

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I'm taking opportunity of this post to ask a question.

Making the piece => one fire

Underglazing => second fire

Transparent glazing : third fire

Oups, my electricity budget is suffering.

So could it we possible to save one firing by underglazing before biiscuit? Which means: making the piece, underglazing then first fire.

Your thought :-)

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