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Underglaze Tissue Paper Saftey

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Does anyone have info...or links to info bout tissue paper underglaze transfer safety and food safety.

I purchased them from a clay supplier...the clerk said under clear they are food safe...

The company that sells them said no, but it seemed the person I spoke with didn't really understand me.



has anyone tested them?

does anyone know?


Any more info than what I have, :blink:  would be appreciated!

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From my understanding, even under glazes listed as "Food Safe" still need a glaze coat over the top, to be used.


What was the misunderstanding, with the manufacturer's rep? I would definitely heed any precautions the maker gives you. They know the most about their own product.

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Guest JBaymore

I'd believe the manufacturer until proved otherwise.


My understanding of this stuff is that just because something is an underglaze or a slip or a wash and it is residing as a separate application under an applied glaze layer, that does not mean somehow inherently it is totally "isolated" from the melting, bubbling, roiling thin glaze layer and then what might potentially leach out of the fired surface (relative to potential "food safety"). 


Generally the higher the firing temperature / cone range, the more there is interaction between the underlying materials and the melting glaze layer.  At the top surface you have "glaze"  at the bottom you have "body".  Somewhere in between there is a no-man's-land that is the intermingling of the body chemistry and the glaze chemistry, as the glaze eats into the body and body grows micro-crystaline materials into the glaze. 


Adding the underglaze / slip/ wash in there just complicates that interaction. How far up toward the surface the materials might migrate is likely dependent on  a myriad of variables for any situation.  How far into the melted glaze surface any acid/base might be able to pull materials out likely is the same.  Add in stuff like pinholes and crazing... and you have a totally variable situation that is case-by-case.


The only two materials that are legally regulated (published standards and procedures for testing required by law) for food use in the USA are lead and cadmium compounds.  The FDA has standards for this and the State of California has more stringent ones.  Info is available from those entities, respectively.  Non-specific to pottery per se, laws that deal with the suitability of a product for its intended use and stuff that deals with product liability can cover any harm caused by any other materials that are not already specifically regulated.


In the specific case of lead and cadmium compounds........ my understanding is that if they are involved in the production of the piece, then you must comply with the FDA and California laws.  That means if you are using slips, underglazes, and so on that contain cadmium (which includes most reds, oranges, and such) or lead, then these laws apply to you.


The ONLY way to know what YOUR stuff is doing is to 'cough up the bucks' and send the representative samples out to a testing lab and have the standard acetic acid leach test done for any oxides that you might have a question about.  The good news is that a LOT of the oxides involved in ceramic chemistry have no documented potential health impacts.  So there are only a few that you even need to be looking at.


To make life simple for yourself, don't use materials on food use products that can potentially and easily cause harm. 


Note that the manufacturers do not indemnify the end user of the product they make.  (Look for the fine print on their websites and in product literature.)  So just because they say "food safe" on their general product literature, that does not mean that if there ever were a problem they would "back you up".  You'd have to defend yourself.  Then you'd have to "go after" the manufacturer if you incurred damages (from a settlement).....with all the legal cost that would entail.


Example of some "fine print" from a manufacturer's website:


"XXXXXXXXX recommends that the producers of any dinnerware for sale submit their production to an independent approved laboratory in order to test for release or leaching of hazardous materials such as lead or cadmium to meet FDA Guidelines in an applicable category BEFORE DINNERWARE IS SOLD. Many variables (such as exact firing temperature, contamination from other ware being fired along with dinnerware, and glazes that may not provide a stable surface adequate for food safety) are factors in whether a specific dinnerware line meets with FDA Guidelines."




"Tableware producers must have all finished ware tested and approved as safe for dinnerware through a certified laboratory due to possible variations in firing temperature and possible contamination."


(The bold and red highlight of the word "must" there is mine.)






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John, your extensive knowledge and willingness to share it is such a JOY (seriously).post-63409-0-32731200-1430536616_thumb.jpg
And I must personally thank you for helping me to decide to never think another thought about ever making anything that anybody anywhere at anytime might ever put their lips to. If they don't try to drink from the cavities in my sculptural pieces, I'm home free.
I've just been invited by a retail shop to make "gear trays" for guys, derived from my chiseled and gouged rectangles, which, with some modification, one could, should one be so inclined, throw a set of keys and change into. Someone suggested I make the basic forms do double duty so maybe I can at least break even on the shipping charges I am paying to bring supplies into the NH wilderness.  :P  


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