Val Posted March 25, 2016 Report Share Posted March 25, 2016 To achieve the colors and detail I want in my non functional work I usually use earthenware clay, BUT for mugs I feel like I need to use 5/6 stoneware so that they are durable. With stoneware,I paint with underglaze on greenware then bisque at 06 , and then apply clear glaze and fire to cone 5. Amaco velvet bright red is giving me fits ! I am using Amaco Sahara H-9 clear dipping glaze. All of the colors are fine except red which is going milky. I know milky usually means glaze is too thick, but some mug handles were a bit on the dry side after firing which tells me the glaze was not thick enough or I did not submerge long enough. After the dryish handles I held in the glaze for count of 3 instead of count of 2 and everything was perfect except red. I'm about to say to hell with stoneware, or at least red underglaze..........but I love red here are some photos........it was hard to get a great picture so I hope you can see what I mean. Link to comment Share on other sites More sharing options...
Guest JBaymore Posted March 25, 2016 Report Share Posted March 25, 2016 Val.... Note that that underglaze is not intended for food service wares. (symbol...... right side of screen) https://www.amaco.com/products/v-387-bright-red-underglaze Check the MSDS for more info to guide as to why. best, .......................john Link to comment Share on other sites More sharing options...
bciskepottery Posted March 25, 2016 Report Share Posted March 25, 2016 John, The link appears to give conflicting info. Agree the underglaze without any clear glaze covering would not be foodsafe. MSDS is rather useless: https://s3.amazonaws.com/amacobrent-staging/home/deploy/amaco/releases/20150421130036/public/ckeditor_assets/attachments/233/msds-v-series-ap.pdf With a clear glaze, it might meet foodsafe standards. And the manufacturer seems to cover that base ("Tableware producers must test all finished ware to establish dinnerware status, due to possible variations in firing temperature and contamination") but they don't make it clear you could/should use a clear glaze. A while back, Tony Clennell ran into a problem with a gallery regarding his use of a zirconium encapsulated stain: http://smokieclennell.blogspot.com/2014/12/gargling-pesticide.html Bruce Link to comment Share on other sites More sharing options...
Guest JBaymore Posted March 25, 2016 Report Share Posted March 25, 2016 If cadmium compounds are present (likely in this kind of a red), in a slip, glaze, underglaze, overglaze, etc, on food contact ware... potters are bound by the US FDA (and California) laws. Not just the glaze. To comply with those you have to test to know that the levels are below the thresholds (which differ for different types of forms). That is why the manufacturers 'hedge their bets'. They don't indemnify the users of their products. A glaze coating over a slip/underglaze, stain etc. doesn't assure that the underlying material is somehow 'isolated' from the surface of that glaze. Particularly at elevated firing temperatures where the interface layer is pronounced. Also the application thickness of BOTH components could then be very involved in any potential issues with release. The only way to KNOW is to have the combination tested in a lab. 99.999999% of the time it likely will be fine. But the laws are the laws. People should know about them. Encapsulated stains are new enough that the laws have not caught up with them (yet). If they ever will. Because MANY people read these threads... of varying experience levels...... I post this kind of stuff. Red can be beautiful. But there is stuff that people should also know about (in case they don't) beyond the 'Mark 1 Eyeball Test'. best, .........................john PS: Yeah... that MSDS is a joke. (Another whole subject!) Wouldn't download when I checked earlier........ had just upgraded to adobe Reader DC...... which screwed up my browser's ability to get pdfs. Link to comment Share on other sites More sharing options...
Val Posted March 25, 2016 Author Report Share Posted March 25, 2016 OOPS I guess I assumed it was the rating of the clear top coat that mattered........Thanks for the heads up Val Link to comment Share on other sites More sharing options...
Pugaboo Posted March 26, 2016 Report Share Posted March 26, 2016 I've been wondering, When you get a piece tested does the report say that all pieces using that glaze are safe or just that one piece that was tested? Also where do you send the pieces to be tested? Been thinking of having a few of mine done since I am finally settling on certain colors and all. I also went to the Amaco site and yes the MSDS sheets are useless (or maybe I just don't know what I am looking at), none of them seem to say anything about any cadmium, they seem to say everything is a-ok to use for pretty much anything. I also looked at the Amaco LUGs as well and that sheet says nothing about dangerous stuff either. I did notice one thing, the LUGs all have the dinnerware safe symbol but NONE of the Amaco Velvets do, I wonder why? Does anyone know? I know a lot of people that use Velvets, I just got some myself and have been doing tests with them. I have until now only used the LUGs but would like a broader color palette. I was told when I first started doing pottery that a clear glaze over an underglaze makes it safe for food, so this is not true? If I didn't read the forum and went by what a teacher told me then went on to read the MSDS sheets I would assume LUGs were food safe, but if they put stuff in that they don't list how other than paying to have each and every piece tested can a potter actually know what is safe and what isn't? T Link to comment Share on other sites More sharing options...
Min Posted March 26, 2016 Report Share Posted March 26, 2016 I’ve sent a few test cups to this place http://www.bsclab.com/Pottery_Testing.html They email you the results in a about a week. You pay for each material you get the sample cup tested for. Fire the test piece with a cone pack next to it and keep that for reference. In theory every time you fire that glaze, or underglaze/slip/engobe glaze combo, you aim for the same cone. Materials can go from underglaze to glaze in the melt so putting a clear over a cadmium ug could still leach in theory, but not likely, have to test to know for sure. I don’t think anything more than that is reasonable. Link to comment Share on other sites More sharing options...
Mark C. Posted March 26, 2016 Report Share Posted March 26, 2016 Commercial reds and yellows and oranges are suspect until proven otherwise Historically their always has been trouble with reds-they are hard to get. at least with my Mark 1 eyeball test Link to comment Share on other sites More sharing options...
GiselleNo5 Posted March 26, 2016 Report Share Posted March 26, 2016 Amaco has a Facebook group called Amaco Cone 5/6. There are admins on there who are potters and very helpful. I dislike Laguna but I do love their Dynasty Red. Lots of photos in my gallery. Someone else recommended Coyote's Really Red, which I plan to try. Link to comment Share on other sites More sharing options...
bciskepottery Posted March 26, 2016 Report Share Posted March 26, 2016 I've been wondering, When you get a piece tested does the report say that all pieces using that glaze are safe or just that one piece that was tested? Also where do you send the pieces to be tested? Been thinking of having a few of mine done since I am finally settling on certain colors and all. Typically, you ask to test for the material that is of concern . . . if the glaze has lots of copper, you test for copper leaching. If the material in a glaze is non-toxic, e.g., iron, there is no need to test for it. Basically, you are testing to see if the glaze is durable and mature at your firing temperature. And, you compare your test results against permissible levels established by FDA, EPA, or local state. For underglazes, the items of concern are typically cadmium and zirconium -- what manufacturers use to encapsulate bright color materials to prevent them from leaching. Testing can be important because glazes and clay bodies, or two glazes overlapping, or glazes and underglazes, interact during firing; while a glaze may appear to be okay from the ingredient list, it may interact with something in the other glaze/clay body/underglaze, to push the glaze over the limit. What makes this most difficult is that we don't have a clear idea what manufacturers put into their commercial products -- so it is hard to test for something we don't know is there. That is why many potters prefer mixing their own glazes as they know and can test for potential problems and compliance with regulations. Even that is not a sure thing as we know suppliers of pottery materials often change composition of basic items, e.g., new custer vs old custer, G200 vs G200HP, old Gerstley vs new Gerstley, etc. Add to that consistency in firing as firing can affect how the glazes/underglazes/clay interact and form. When your kiln is not reaching full temperature, you underfire and that can allow more leaching of potentially bad things. Controllers help minimize this, but you have to keep your kiln in good shape. Cutting corners on kiln maintenance may save you pennies now, but could create problems later if you are a seller. Link to comment Share on other sites More sharing options...
Val Posted March 26, 2016 Author Report Share Posted March 26, 2016 I am still curious about why the clear glaze is a bit milky only on Amaco velvet red and not other colors Link to comment Share on other sites More sharing options...
Pugaboo Posted March 26, 2016 Report Share Posted March 26, 2016 I've emailed BSC Labs asking for current prices for testing for cadmium and lead. I'm primarily concerned about cadmium since I think lead is used way less and cadmium is used more frequently than I realized in the encapsulated form. Visited the FDA pages on these two things as well. I was looking for the how close to the rim something can be used guidelines but didn't find them. I do a lot of hand painting with Underglazes then clear glazing on mugs so this is an area I am particularly interested in. I usually glaze the interiors of these items in Coyote White. I never use a bright red glaze on the interior of a piece but I do silkscreen little red underglaze hearts on some things that are then clear glazed. I am assuming I would make a test cup with the design on the inside rather than the outside to send to the lab yes? Will have to look at some of my other items and decide if I need to change how they are glazed, or decide I want to keep using them as is and send them for testing. I am hoping it's not too expensive. In all the years I've been buying and collecting pottery for my personal use from potters I never once thought about stuff like this. Recently I was at a festival and visited another potters booth and recognized a glaze on some pieces that I know is not considered food safe and was told it's safe as long as it's fired again with a clear glaze over the top. Huh. I wonder how many potters have been told the clear glaze rule making stuff food safe when they are starting out and never question it isn't so. Off to do the lemon test on some pieces while I wait to hear back from the lab. T Link to comment Share on other sites More sharing options...
Guest JBaymore Posted March 26, 2016 Report Share Posted March 26, 2016 I've been wondering, When you get a piece tested does the report say that all pieces using that glaze are safe or just that one piece that was tested? Also where do you send the pieces to be tested? Been thinking of having a few of mine done since I am finally settling on certain colors and all. What you get there is a "representative test". If the applications of the glaze/underglaze (etc.) are typical of the applications in production, AND the glaze/underglaze is on the SAME clay body, AND the firing in all parts of the kiln is the exact SAME cone and atmosphere... then that test will be representative of that particular situation. Change any of those above things, and the validity of the test results to the other object is "suspect". You are not only making sure that you are OK in this department for yourself, you are establishing a 'paper trail' of "due diligence" in the quite UNLIKELY event that there might ever be an issue of some sort. The smartest thing to do to 'cover your butt' and also to protect your customers is to not use a glaze on food contact surfaces that has anything in it that could possibly cause issues. So to do that you have to know what is in there... AND.... know something about potential toxicity issues. So some good ole' research and education is likely in order for some folks who have not yet dealt with this more technical side of ceramics. A nice kinda' generic white-ish liner glaze is the solution that many potters choose to use. There is a reason. As has already been said here, commercial glazes are potentially an issue... because you have trouble establishing what is actually IN there... AND....... because the manufacturers do not indemnify you as a manufacturer yourself (in the production of your own wares). Luckily, most of the materials we use in glazes are either things that are pretty non-toxic or that are in forms that are not toxic. For example, ingesting silica and alumina (the core constituents of a glaze molecularly) is not an issue. Ditto most other common stuff in base glazes. The places of any concern (and that concern CAN easily be overblown) typically are in the category of coloring metals and also a couple of reasonably well known 'problem' items, like lead and potentially barium. In the coloring metals department, iron is a pretty generally 'safe' one. Zirconium compounds to make whites (opacify) is also a typically good choice. As to where to get stuff tested.... for us studio artists the really most convenient place is the Brandywine lab that Min posted the link to. The often cited "Alfred Analytical" no longer exists. Most commercial manufacturers have in-house labs where they can test inexpensively and often. best, ....................john Link to comment Share on other sites More sharing options...
Guest JBaymore Posted March 26, 2016 Report Share Posted March 26, 2016 I was looking for the how close to the rim something can be used guidelines but didn't find them. I do a lot of hand painting with Underglazes then clear glazing on mugs so this is an area I am particularly interested in. Lip and rim: http://www.astm.org/Standards/C927.htm Considered the top 20 mm both inside and out. -SGCD- Washington DC. best, .................john Link to comment Share on other sites More sharing options...
bciskepottery Posted March 26, 2016 Report Share Posted March 26, 2016 I am still curious about why the clear glaze is a bit milky only on Amaco velvet red and not other colors Your red is covering a lot of area, so the thickness of the red underglaze may be a factor; also, you said the handles were rough -- which could mean you are underfiring at cone 5 (maybe a cool cone 5 vs a hot cone 5 or 5.5. Milky could be both thickness and underfiring. Were the other colors used to cover similar large surface areas? Or just used for decoration with a lot of white stoneware with just clear? Rather than spend a lot of money on underglazes for those interiors, consider making a slip of your clay body with red mason stain and apply that at leatherhard stage. Link to comment Share on other sites More sharing options...
Pugaboo Posted March 26, 2016 Report Share Posted March 26, 2016 Thanks John! I am going to have to do some thinking on all this. How common is cadmium leeching in encapsulated glazes? Might have to switch to only using white on any food surface, which removes a lot of forms from use. Will have to wait until I get a price from the lab. If I can't afford the testing I might have to consider quitting and getting a real job. Its all very depressing. T Link to comment Share on other sites More sharing options...
Guest JBaymore Posted March 26, 2016 Report Share Posted March 26, 2016 The testing is pretty inexpensive. Testing for one constituent will typically set you back under $75.... not counting shipping and the item itself. Adding items to extract in the tests increases it about $30 per item. William Carty (Alfred engineering school tech 'guru') had some interesting updated info on potential cadmium leaching from encapsulated stains at his presentation at NCECA this past month. I'll wait to see if he posts more online resources and get something pointing to it. But since the stain can be put into ANY suspending mixtures by the end user and fired in most any way... I think that "total guarantees" no matter what..... would be hard to give. Too many potential variables. Product liability insurance for potters is quite inexpensive (see Potters Council, CERF, and American Craft Council for coverage) . You can get $2 million in coverage for less than $1000 a year and that includes stuff like premises liability. That should tell you something about the frequency of "issues". best, ........................john Link to comment Share on other sites More sharing options...
Min Posted March 26, 2016 Report Share Posted March 26, 2016 Don't get depressed Terry, last time I got a sample tested there it was about $20 - $25 for a single ingredient. Buys you a lot of piece of mind. Link to comment Share on other sites More sharing options...
Pugaboo Posted March 26, 2016 Report Share Posted March 26, 2016 John - $75 is more than I can afford for each item right now. $1000 is a high amount for the insurance for me as well. I am just starting out and have not yet gotten to the level of a real pottery business yet. Everything is $100-1000 to step up to the next level. I'm studying, researching and reading as much as I can as fast as I can. Its sooo much easier to slap some paint on a canvas and sell it, but people aren't looking for non functional as much any more. I tell myself baby steps to get there but something's just throw me for a loop and make me question whether I can get there in baby steps. Min - That is more in the range I can afford. Thank you for letting me know an approximate cost. That gives me some hope and testing a piece with the red hearts would be priority. T Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted March 26, 2016 Report Share Posted March 26, 2016 *Edited* John explained the same thing I just wrote clearer, I completely missed that paragraph when I wrote this stuff. Pugaboo, Don't give up because of a few test in your way. Your work is awesome! Don't get defeated over a few regulations adapt, test, and get past those simple limitations and profit! Link to comment Share on other sites More sharing options...
Min Posted March 26, 2016 Report Share Posted March 26, 2016 Ouch, I hope it hasn't gone up to that much. My figures are what I remember from when I sent the last test cup in about 8 years ago. At 75- I would still do it if using cadmium on food surfaces. Is this something the Potters Council could negotiate a discount for with one of the labs? A central pool of information from people willing to share their results / recipes / firing schedules etc would be helpful. Link to comment Share on other sites More sharing options...
Pugaboo Posted March 27, 2016 Report Share Posted March 27, 2016 If it's $75 I'm going to have to do some saving and then test my #1 seller then save and do the next one, etc. I'm ok with that, just need to quit panicking over theta ought of the cost of doing all the glazes and then the Underglazes. For some things that I can't figure out if the glaze has cadmium or not I am going to look at what it does to the pieces to use a white liner glaze instead. Only thing can't do much about is plates but will do some thinking on them as well. Wish the MSDS sheets were a bit clearer to me but have downloaded a few and am studying and googling the different words, I'm not a scientist. LOL Making the pieces to test will take some thinking as well. I need to figure out how to silkscreen and handpaint on the inside of a small straight sided cup, I am hoping they will tell me a small bowl or plate will be ok instead since I need to make them the same way as I do normally. I hope everyone has a wonderful Sunday, me I am going to spend it in the studio painting some new designs I have been working on and stop freaking out over the stuff I can't do anything about at the moment. Keep telling myself baby steps BABY STEPS. T Link to comment Share on other sites More sharing options...
Guest JBaymore Posted March 27, 2016 Report Share Posted March 27, 2016 No reason to 'freak out'. As you say... one step at a time. The odds on it being a problem with such small coverage of the pieces with anything that COULD potentially be a leaching problem seriously lessens the likelihood it'll ever be an issue. The fully bright red interiors of the original mugs is what 'got my attention'. Lots of food contact surface area is there. That increases the amount of material that could be an issue. Study some about the development of color in ceramics... and you can start to understand which commercial glazes MIGHT have stuff in them of potential concern. Example: Very bright reds (other than reduction copper reds), oranges, and yellows are all likely to contain cadmium in one form or another. But not always for duller color reds. Bright reds at china paint temps can be lead and iron (the classic "Kutani red"). Chrome/tin pinks are another way to get a reddish tone. So it is not always cadmium present. best, ...................john Link to comment Share on other sites More sharing options...
Pugaboo Posted March 29, 2016 Report Share Posted March 29, 2016 Wanted to update anyone following this topic... I just heard back from the lab and it looks like the fee for testing for Cadmium will be less than $20 plus postage. They can test for all kinds of other thing bugs as well. That price was so great to read! I plan to send in a couple of small pieces as soon as I can. T Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted March 29, 2016 Report Share Posted March 29, 2016 Glad it worked out for you. That price is fantastic! I bet your test will come back fine and you will have the paperwork to back it up! Link to comment Share on other sites More sharing options...
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