Rare metals in glazes

[Joe LS]

This is my first post here, and with a few narrow exceptions I am new to ceramics. My background is in isotope chemistry and paleontology, both of which have little but not no overlap with ceramics.

I have two questions. First, has anyone here experimented with using rare metals in glazes. I'm sure that there are some discussions here of silver, gold, and platinum (although I could not find them), and am playing with silver (see attached pic, where I tried to use silver to create the effect of a starry night with an aurora), but what I'm really interested in is even rarer metals: especially ruthenium, rhenium, iridium, and osmium. None of these metals will melt, even at cone 10, but all produce volatile (and toxic) oxides at  much lower temperatures-- at room temperature in the case of osmium powder. The oxides are not so toxic that they cannot be safely removed with a good ventilation system, and once out in the air they quickly form insoluble complexes that render them harmless. What I'm wondering is whether, rather than being released, some of the oxides will dissolve in a molten glaze, and if so if there is a glaze material that is particularly good at this. Whatever it is must have a fairly low melting point, as the metal oxides decompose back to metal and oxygen at higher temps.

My second question is whether anyone has tried electrolysis of molten glazes during firing? I tried it with silver, to see if I could get silver crystals to grow in the glaze. It didn't work. But it seems like something that could be used to do things like control  color by controlling the oxidation state of metals.

These are open ended questions. I'm interested in comments and discussion from and with like minded people. Thanks

[liambesaw]

Lustre overglazes can be made with many metals.  In fact, commercial ones are made with rhodium or iridium salts in order to make the finish durable. Bismuth salts are also present to flux the specular films into the glaze surface.  Last summer I was experimenting with making a specular silver lustre and got very close, hoping to get back into it this summer when I have more free time.

[Joe LS]

Thanks for commenting. I know about the use of metals for lusters, but I'm more interested in what happens at depth, and especially in the interaction between metallic metal and the surrounding melt. So, for example, in the glaze in the picture you can see where beads of metallic silver have partly dissolved to create streaks and halos of green. I like that effect. But metals like ruthenium and osmium will not melt to form nice shiny beads. They will dissolve, however, and it's control over that dissolution that I want to achieve. Ruthenium tends to produce red. You can imagine how a glaze containing Ru powder could produce red spots, a mottled red, or uniform red, depending on how soluble metallic Ru is in the melt. Conceivably (and I just thought of it, which is why it contradicts what I say above) these metals could become saturated in a melt, and then grow as metallic crystals as the melt slowly cooled.

I am especially curious to see what osmium does, as I really doubt anyone has ever used it in a glaze. I can't even find any information on the color of Os in aqueous  solutions. It has 8 known oxidation states form 2- to 8+, so it should be fun to play with IF there is a glaze that will capture its toxic oxide.

[liambesaw]

9 minutes ago, Joe LS said:

Thanks for commenting. I know about the use of metals for lusters, but I'm more interested in what happens at depth, and especially in the interaction between metallic metal and the surrounding melt. So, for example, in the glaze in the picture you can see where beads of metallic silver have partly dissolved to create streaks and halos of green. I like that effect. But metals like ruthenium and osmium will not melt to form nice shiny beads. The will dissolve, however, and it's control over that dissolution that I want to achieve. Ruthenium tends to produce red. You can imagine how a glaze containing Ru powder could produce red spots, a mottled red, or uniform red, depending on how soluble metallic Ru is in the melt. Conceivably (and I just thought of it, which is why it contradicts what I say above) these metals could become saturated in a melt, and then grow as metallic crystals as the melt slowly cooled.

I know metal oxides like molybdenum, and manganese and others can incorporate into zinc silicate crystals during a crystalline firing, but those are zinc crystals seeded by titanium dioxide and simply colored, not the metal crystals themselves. In saturated glazes (high metal oxide) you can grow iron and manganese crystals, but it would be really cost prohibitive to make a saturated glaze with any of those platinum group metals.

[glazenerd]

Joe:

i have firedmost rare earth oxides: prasdyium, holium, yttrium, neodymium, and a few others- along with silver nitrate. (Love how spell check changes when I try to type them)  You said the key phrase "oxidation state."  FeO4 to FeO, etc. You will find the oxidation state most relative to ceramics and glazes. "Redox " is your starting point, and from there oxidants and reductants. UC Berkeley came out with a Reduction Potential Chart years back for the various metalloids commonly used in ceramics. You can find that chart and discussion in this thread- 

Jim Fox at RiverPottery does silver nitrate reduction firing: his earlier background doing reduction firings before his obsession with crystalline glaze. As mentioned; bismuth is often used but I find vanadium pentoxide far better for oxidation ( not food safe)  Vandium has an O5 lattice, but I have been looking at silica polymorphs with O chains up to O(52). Relative to crystalline glazes, not sure of any other applications. I know of a few who have tried gold and yellow cake (not food safe). I have little doubt that somewhere in the world; some Potter has fired every element they could find. 

Tom

[Joe LS]

Using platinum group metals is not absurdly expensive. Ruthenium is about $9/gram , osmium about $13, and the rest, except rhodium, about $40. Rhodium is the only one that is really out of range. You can do small test pieces with much less than a gram, so it might cost $20-30 (for Ru and Os) to see if you can do something beautiful or fascinating. Then you can decide if you want to put 5-10 grams into making something larger. Of course you probably could achieve the same thing  or something close with cheaper metals (I worked on iron chemistry for years and know what it can do), but the rarity is part of the appeal. In color differences etc you are actually seeing chemistry. It provides a much more complete portrait of a metal than a simple bead or ingot. That's really what I'm aiming for. The glaze is everything. I'm making nothing but simple round, slightly concave plates to put it on, perhaps with  small flanges to hold electrodes.

[liambesaw]

17 minutes ago, Joe LS said:

Using platinum group metals is not absurdly expensive. Ruthenium is about $9/gram , osmium about $13, and the rest, except rhodium, about $40. Rhodium is the only one that is really out of range. You can do small test pieces with much less than a gram, so it might cost $20-30 (for Ru and Os) to see if you can do something beautiful or fascinating. Then you can decide if you want to put 5-10 grams into making something larger. Of course you probably could achieve the same thing  or something close with cheaper metals (I worked on iron chemistry for years and know what it can do), but the rarity is part of the appeal. In color differences etc you are actually seeing chemistry. It provides a much more complete portrait of a metal than a simple bead or ingot. That's really what I'm aiming for. The glaze is everything. I'm making nothing but simple round, slightly concave plates to put it on, perhaps with  small flanges to hold electrodes.

I only meant it's cost prohibitive to make a saturate glaze with them.  So in a 100 gram sample having 20-60% of the glaze be the metal, like in an iron or manganese saturate.  You obviously can't make a similar glaze with platinum group metals since it would be difficult to oxidize them.  But you could of course try using their salts.

[Joe LS]

I was worrying about opposite, about not getting enough to go into solution. Solubility of metallic platinum group elements in pure silicate melts is quite low, in the range of 10-20 ppm, depending on the oxygen fugacity. In soda and other silicate glasses it is higher, but only up to about 100ppm. But the oxides can be quite soluble, and all of the PGMs oxidize in air at fairly low temperatures (Os powder at room temperature) from what I have been able to learn (some aspects PGM chemistry are closely held secrets) these oxides also have fairly low decomposition temperatures, within reach of a kiln. So, in contrast to what I wrote above (I'm thinking this through as I go) PGMs may crystallize out of the glaze as metals not when the glaze cools but when it is warming, as the oxide decomposition temperature is reached. At any rate, there is plenty here to experiment with, using tiny test pieces, and maybe XRD.

[liambesaw]

11 minutes ago, Joe LS said:

I was worrying about opposite, about not getting enough to go into solution. Solubility of metallic platinum group elements in pure silicate melts is quite low, in the range of 10-20 ppm, depending on the oxygen fugacity. In soda and other silicate glasses it is higher, but only up to about 100ppm. But the oxides can be quite soluble, and all of the PGMs oxidize in air at fairly low temperatures (Os powder at room temperature) from what I have been able to learn (some aspects PGM chemistry are closely held secrets) these oxides also have fairly low decomposition temperatures, within reach of a kiln. So, in contrast to what I wrote above (I'm thinking this through as I go) PGMs may crystallize out of the glaze as metals not when the glaze cools but when it is warming, as the oxide decomposition temperature is reached. At any rate, there is plenty here to experiment with, using tiny test pieces, and maybe XRD.

I was able to get a silver specular film as low as 250c by making silver decanoate and silver stearate, but it wasn't durable because the bismuth hadn't had a chance to flux.  Perhaps making a metal soap like that would be an option for you as well.