glazenerd Posted July 7, 2016 Report Share Posted July 7, 2016 From the University of Stockholm, Sweden. 85 pages ( 40 actually/ written in English and Finnish?) not sure of the language-sorry Explores several methods of obtaining reds through glaze chemistry without using lead/s. kth.diva-portal.org/smash/get/diva2:11081/FULLTEXT01 Friend in CA sent it to me... extensive read, best to download and digest slowly. Nerd Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted July 7, 2016 Report Share Posted July 7, 2016 Will have a read tomorrow Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted July 7, 2016 Report Share Posted July 7, 2016 Will have a read tomorrow Same Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted July 8, 2016 Report Share Posted July 8, 2016 I had a read as good as I could, still over my head with most of the tests but interesting trying to work out what the actual process is for making colours. Never heard of striking glass before so that could be an interesting route to go with glaze too. Link to comment Share on other sites More sharing options...
glazenerd Posted July 8, 2016 Author Report Share Posted July 8, 2016 Never heard of striking glass before so that could be an interesting route to go with glaze too. Tile 1 is after 1350F strike fire/30 min hold. Tile 2 is original color before striking. (Note 3% titanium dioxide added to original glaze.) Tile 1 is the strike fire results, Tile 2 is the same tile 2 above: acid etched for 72 hours And one for Joseph - adding 4% molybdenum does interesting things to glazes at cone 6 Nerd Link to comment Share on other sites More sharing options...
MatthewV Posted July 10, 2016 Report Share Posted July 10, 2016 Why 1350°F? Would adding a hold at this temperature on a regular firing do anything? Link to comment Share on other sites More sharing options...
glazenerd Posted July 10, 2016 Author Report Share Posted July 10, 2016 Matthew: in the glass arts: 1350F is the slumping temp, and 1475F is the fusing temp. So the 1350F temp is just enough to soften the glaze without altering it's strength. Copper is the most reactive, then iron: not much effect on cobalt and manganese. I have tested them all. In addition, a titanium dioxide source makes the strike firing all the more dramatic. TiO2 should be a minimum of 3%, and upwards of 8%. Strike firing is commonly used with crystalline glaze to produce dramatic color shifts. Nerd Edit: the longer the hold, the more dramatic the effect. Caution: hold too long and it will pit the glaze. Would adding a hold at this temperature on a regular firing do anything? I have crystalline friends that have tried it with limited results, not nearly as dramatic. Tile 2 above is 1% each of copper carb and yellow iron. 3% TiO2 was also used. Link to comment Share on other sites More sharing options...
jpdes Posted July 12, 2016 Report Share Posted July 12, 2016 Strike firing glazes is an interesting concept. Glazenerd, do your time/temperature descriptions refer to an eg. 30 minute hold at 1350F on the cool down from a glaze firing or an entirely separate firing starting with cold, glazed ware? Would it matter which approach was used? Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted July 12, 2016 Report Share Posted July 12, 2016 Very nice colours on the strike firing. I had seen this change happen with iron glazes when firing decals at 800c~ which is about the 1350f. Interesting results with the crazing too. It's amazing that things are happening and moving around even at that temperature. Jpdes, from the conversation above it seems a completely new firing although some have tried on the way down with limited success. Would adding a hold at this temperature on a regular firing do anything? I have crystalline friends that have tried it with limited results, not nearly as dramatic. Tile 2 above is 1% each of copper carb and yellow iron. 3% TiO2 was also used. Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted July 12, 2016 Report Share Posted July 12, 2016 Yes is this firing separate or a hold on the way down. I am curious now to try this. Link to comment Share on other sites More sharing options...
glazenerd Posted July 12, 2016 Author Report Share Posted July 12, 2016 Strike firing is a separate firing after the glaze firing. 1350F, with a maximum of 30 min. hold. Copper and Iron is the most reactive colorants to a strike fire. If you really want drama in colors: 3-8% titanium is required. 8% TiO2 in a reduction strike will turn purple-very cool stuff. Fire in oxidation first: then strike fire in either oxidation or reduction. Reduction strike is even more dramatic in some cases. Nerd Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted July 13, 2016 Report Share Posted July 13, 2016 Very interesting. I have some modifier glazes that I use that have very high titanium. I will try this strike firing on some pots in the future. Actually I think I might just run a strike fire tonight. I am bored and I have somewhere I have to be somewhere tomorrow all day. Strike fire time? Link to comment Share on other sites More sharing options...
terrim8 Posted July 13, 2016 Report Share Posted July 13, 2016 What is the form of the molybdenum? Link to comment Share on other sites More sharing options...
glazenerd Posted July 13, 2016 Author Report Share Posted July 13, 2016 What is the form of the molybdenum? > sulfide Interesting result> looks like a crawl glaze, but it is smooth. Nerd Link to comment Share on other sites More sharing options...
Dick White Posted July 13, 2016 Report Share Posted July 13, 2016 What do you think would happen if you strike fired an acid-washed piece? Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted July 13, 2016 Report Share Posted July 13, 2016 Is the titanium playing a similar role to tin in the red glazes? Am I right in thinking you are getting Cu3+ to Cu2+ and the extra reduction is going to Cu1+ Cu? It's all far too complicated, I have been thinking about this for the past week and I always feel like I know less than when I started. It was all so simple with a glaze recipe. Link to comment Share on other sites More sharing options...
glazenerd Posted July 13, 2016 Author Report Share Posted July 13, 2016 What do you think would happen if you strike fired an acid-washed piece? Did several tests with acid soak, then a strike fire. Scumming, pitting, rather unattractive and unappealing finish. Joel: I am still trying to find my last test piece with samarium, yttrium and iron: that started popping cherry red spots I had to trash it, not realizing it was one I wanted to keep. I still have my notes though. Titanium has one of highest refractive indexes, I know that also plays a role. Nerd Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted July 14, 2016 Report Share Posted July 14, 2016 copper does NOT exist as a Cu3+. only Cu1+ and Cu2+ check your electron distribution charts. LT Link to comment Share on other sites More sharing options...
Dick White Posted July 14, 2016 Report Share Posted July 14, 2016 What do you think would happen if you strike fired an acid-washed piece? Did several tests with acid soak, then a strike fire. Scumming, pitting, rather unattractive and unappealing finish. Nerd ok, that answers that. Did you try the other direction - acid etching a striker? Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted July 14, 2016 Report Share Posted July 14, 2016 Oh no Cu3+ Now I am stumped about the colour change. What is changing between the first firing and the second Link to comment Share on other sites More sharing options...
Magnolia Mud Research Posted July 14, 2016 Report Share Posted July 14, 2016 Joel, My understanding is that the term "striking" may mean reheating the pieces to an intermediate temperature with reduction taking place during the "hold" period, or just reheating without a reduction atmosphere. I'm never sure which meaning is being discussed by potters. When our studio was firing at cone 3 oxidation in a gas kiln we often "struck" the work when it cooled to a red color by turning on the gas and operating with a reduction atmosphere for about 15 - 30 minutes. The glazes containing copper would turn red. If we refired the struck pots in an oxidation mode, the red would disappear and be green. This was especially effective if you made marks with copper carbonate "ink" over another glaze. Without striking, the marks would be green or if very thin marks they would not show at all.) This implies that the red is due to a surface reaction that reduces the Cu2+ to Cu. The carbon monoxide from the reduction atmosphere will diffuse into the surface layer (couple of microns) of the glaze and reduce the Cu2+ to Cu. To penetrate to the deeper layers requires much longer exposure (depth proportional to the square of time; i.e. to double the depth you must wait 4 times longer). Not mentioned in the thesis Nerd referenced is that the glass must be slowly cooled through the glass transition region to allow the copper atoms to form a cluster. Other work on copper red glazes has shown that draw rings pulled from a kiln at cone 10 reduction show no color when quenched but will become red if reheated to above the glass transition and held there for several an hour or so. Slow cooling is a must for copper reds, as well as other glaze types (crystalline for example). The effect is due to movement of cations in the melt/glass to form aggregates that create new phases and/or change the optical properties of the glassy material. A good place to start for more insight is the book "Silicate Glasses and Melts" by Mysen and Richet. For the diffusion aspect: "Geochemical Kinetics" by Zhang. Be prepared for a very different vocabulary in both sources. LT Link to comment Share on other sites More sharing options...
glazenerd Posted July 14, 2016 Author Report Share Posted July 14, 2016 Did not realize so many would be interested in strike firing and acid etching: so I will do a bit of an information dump to help you along. To clarify: all samples shown were fired in oxidation and struck in oxidation. One caution I need to make first: USE SAFETY GLASSES AND GLOVES WHEN HANDLING ACIDS, ADEQUATE VENTILATION IS ALSO REQUIRED. Do not store acids where children can access them. Strike firing in oxidation at 1350F 1. control piece. 2. 10 min. hold 3. 20 min. hold 4. 30 min. hold. 1% copper carb/1 MNO / 2% titanium Acid etching with 72 hour soak/ no strike 1. control 2. muratic 3.sulfuric 4. potassium hydroxide. (acids mixed 2 water to 1 acid. (2% cop. black 3% titanium dioxide) Nerd Link to comment Share on other sites More sharing options...
Joseph Fireborn Posted July 15, 2016 Report Share Posted July 15, 2016 I did a strike fire on some of my pots with iron, I didn't notice any difference. I will try it on a copper glaze when I get one made up. I don't know if I did it right or not. I held at 1360F for 30 minutes. Maybe I need a longer hold. But like you said, these glazes didn't have any copper or titanium in them, so I will wait and try again when I have some glazes with those materials in them. Either way your results are interesting. Link to comment Share on other sites More sharing options...
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