Libba Adams Posted March 13, 2021 Report Share Posted March 13, 2021 Hi everyone! My first posting. I am looking for a black satin matte glaze that is stable and safe as a liner glaze in ^6 ox. I have 1000g of Stephen Hill’s Frost Black Satin Matte to test but I’m unsure of its safety due to 9.2 % zinc,3%manganese dioxide and 1.8.% copper oxide in the contents. Thanks! Link to comment Share on other sites More sharing options...
Min Posted March 13, 2021 Report Share Posted March 13, 2021 Could you post the recipe? I'm not keen on using satin glazes as liners. (or using copper and manganese in them) Welcome to the forum Link to comment Share on other sites More sharing options...
liambesaw Posted March 13, 2021 Report Share Posted March 13, 2021 Copper and manganese are safe (at these levels) as long as the glaze is fired to maturity and durable to acid and alkali. But we can't offer opinions on the durability of the glaze without seeing the rest of the recipe. Satin matte is a poor functional surface due to the likelihood of utensil marking and difficulty of cleaning Link to comment Share on other sites More sharing options...
Libba Adams Posted March 13, 2021 Author Report Share Posted March 13, 2021 Thanks, everyone. Here's the recipe: ( I forgot to mention the Cobalt Oxide in my question) Stephen Hill's Frost Black Satin Matte Neph Sye 31.8, Silica 22.7, Whiting 22.7, Ball Clay 13.6, Zinc Ox 9.2, Black Iron Ox 4.3, Manganese Dioxide 1.8, Cobalt Ox 3, Copper Ox 1.8 Makes sense that it might show markings and be difficult to clean, but my memory of it was that it was a very buttery soft black and seemed more durable than many matte glazes feel. I'd love to have recommendations for black ^6 ox glazes that work well on dinnerware but are not very glossy. Thanks! Link to comment Share on other sites More sharing options...
liambesaw Posted March 13, 2021 Report Share Posted March 13, 2021 Here's the analysis. Food safety is likely,may want to do a durability test with lemon or vinegar. May craze on porcelain. Link to comment Share on other sites More sharing options...
Libba Adams Posted March 14, 2021 Author Report Share Posted March 14, 2021 Thank you so much!! Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 14, 2021 Report Share Posted March 14, 2021 51 minutes ago, liambesaw said: Here's the analysis. Food safety is likely,may want to do a durability test with lemon or vinegar. May craze on porcelain. @Libba Adams It’s sort of a Bristol glaze which are a bit quirky. They were an early way to get to cone six and usually required 0.2-0.4 zinc in a .7 RO base. With about an 8:1 si:al ratio we would expect it to fire glossy so there is the chance that it is matte because it is under fired a tad. It has low alumina as that was a way to get things to fire lower back in the day. An R2O:RO of 0.2:0.8 is in a known durable range. Lots of colorants so I would check it’s durability, dishwasher is probably one of the most aggressive with respect to glaze. Metal marking may be a non issue really Link to comment Share on other sites More sharing options...
Min Posted March 14, 2021 Report Share Posted March 14, 2021 I would not expect that to be a durable non leaching glaze. Silica is way too low and alumina is on the low side. The foundation of a durable glaze is to have enough of both silica and alumina in the glaze. Combine this with 3 cobalt oxide plus the 1.8 copper oxide and manganese I personally wouldn't use this glaze. Have a look at the targets below, last 2 rows in both charts, see how the silica for mid range glazes has a minimum of 2.4 or 2.5, compare that to your levels, (blue box in Liam's post above), this glaze has 1.7 silica. One more set of limits, this one from Hesselberth and Roy, their recommended minimum silica level is 2.5 also. Link to comment Share on other sites More sharing options...
oldlady Posted March 14, 2021 Report Share Posted March 14, 2021 when you get to the testing stage, check the surface for fingerprints. when i was working at the frederick, md. potters' guild shop, there were stacks of gorgeous black matte pieces. every time anyone touched them i had to wash them off. beautiful? yes, practical, no. if you try using a matte on an interior, try scraping a spoon on the surface. you might understand why they are impractical. the sound of nails on a chalkboard comes to mind. Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted March 14, 2021 Report Share Posted March 14, 2021 What you want to find is a satin/glossy on edge of the transition liner, not a matte black liner. It is close enough and it will match if you put a matte black on the outside and durable enough to not cutlery mark. Customers won't be disappointed because the inside of a satin/glossy bowl/cup/plate will be better to use than a matte one anyways. Finding a matte black liner glaze that stands up to cutlery, staining, and leaching is going to be pretty difficult if not nigh impossible. You will need a perfect glaze combination on the exact edges of satin/matte and then you will need a firing that doesn't slow cool to much and also doesn't cool to fast. It won't be worth the effort if you want to sell pieces that are reliable and long lasting. Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 14, 2021 Report Share Posted March 14, 2021 3 hours ago, Libba Adams said: I'd love to have recommendations for black ^6 ox glazes that work well on dinnerware but are not very glossy. Thanks! Not to worry , spray them with black underglaze and glaze with a durable true matte clear. True mattes will go from matte to gloss just by adding more silica so you can texture to your taste so to speak. Satin is just a level of gloss or matte if you will, so you can adjust to your preference with a durable true matte and make it any level between matte and gloss just by adding silica. Metal marking is more common with abrasive oxides such as zircopax which microscopically roughen the surface and are happy to grind the edge off your knife. Clear mattes quite often don’t metal mark, been trying to mark a true matte cup I have sitting here for the last half hour - can’t get it to mark. Link to comment Share on other sites More sharing options...
Libba Adams Posted March 14, 2021 Author Report Share Posted March 14, 2021 This is good info. Do you suggest mixing your own black underglaze, and if so, so you have a favorite? Thanks! Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 14, 2021 Report Share Posted March 14, 2021 5 hours ago, Libba Adams said: This is good info. Do you suggest mixing your own black underglaze, and if so, so you have a favorite? Thanks! I don’t, it’s a lot of work with minute quantities of stain, clay etc... There are many commercial underglazes out there often made with encapsulated stains so inherently pretty stabile. Link to comment Share on other sites More sharing options...
Libba Adams Posted March 14, 2021 Author Report Share Posted March 14, 2021 Makes sense to economize on the time/effort! I’m leaning away from the black now. I’m just coming back to my studio after a few years being a caregiver, so am trying to develop a palette that works. Maybe it’s time to focus on Temmokus! Link to comment Share on other sites More sharing options...
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