Warm Glass - Electric Mid&Hi Fired Ceramics2024-03-28T19:42:35Zhttps://cone6pots.ning.com/forum/topics/warm-glass?commentId=2103784%3AComment%3A130847&feed=yes&xn_auth=noKaren, If you have not miste…tag:cone6pots.ning.com,2016-08-06:2103784:Comment:1364632016-08-06T19:19:13.761ZNorm Stuarthttps://cone6pots.ning.com/profile/NormStuart
<p>Karen, If you have not misted fused glass with a solution of Borax, I think you'd be impressed with the results. With some experience now I've found after a tacking fire followed by a slump firing many transluscent colors lose their sheen. Misting them first with water with as much Borax as will dissolve adds sodium and boron flux to the surface of the glass.</p>
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<p>This very inexpensive mixture is sold at a hefty cost as "Devitrification Spray" and "Super Spray". Boron is a glass…</p>
<p>Karen, If you have not misted fused glass with a solution of Borax, I think you'd be impressed with the results. With some experience now I've found after a tacking fire followed by a slump firing many transluscent colors lose their sheen. Misting them first with water with as much Borax as will dissolve adds sodium and boron flux to the surface of the glass.</p>
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<p>This very inexpensive mixture is sold at a hefty cost as "Devitrification Spray" and "Super Spray". Boron is a glass as well as a flux and the Sodium and Boron in the Borax is fully melted and bonded as part of the Bulkseye glass, likely well below our speak slumping temperature of 1,050.</p>
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<p>It's likely our 1,050 F is actually a true 1,250 or 1,350. I needed to adust our temperatures down to acieve the various tack, fuse and full-fuse results and also slow the heating ramp to avoid cracks. It's likely this could be the result of using a spacer which leaves only 3/4 inch of our platinum thermocouple tube exposed in our kiln to make loading and unloading the kiln easier. The drawback is the thermocouple perhaps responds to temperature changes slower than it would if a full 1.5 inches were exposed to the heat.</p>
<p>I plan to try this spray on cone 6 glazes when they are subsequently refired to cone 06 after adding low-fire glaze. This second firing often leaves the cone 6 glaze somewhat dull from devitrification.</p>
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<p>I'm also impressed with the shockingly costly ZYP boron nitride release spray. While it's $54 per 13 oz aeresol can. I tried another brand Slide Hi-Temp 1800 for half the price which really doesn't work. They're both boron nitride with 1% talc and a butane gas, but somehow the implementation is quite different.</p>
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<p>I've also tried three other shelf and mold resists:</p>
<p>1.) Calcium carbonate on flat shelves as a resist but i found I needed to wet it first to tool it flat.</p>
<p>2.) Alumina, suggested by a clerk at a Bullseye store, but I can only guess he had never tried that himself as it embeds into the glass, frosting it completely.</p>
<p>3.) Also the commercially sold kalin with pottery plaster resist, but did not like repairing the flaking after each firing. I mixed my own using calcined kaolin but the Glomax brand calcined kaolin left too much texture on the glass due to granularity.</p>
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<p>I was interested in a video on YouTube showing the lost wax casting of a three inch thick globe. Likely to release bubbles and annealing time the video showed the artist starting the kiln then unloading it, with a caption "Three Weeks Later" ! ! Wow. Dicroic clear does help prevent bubble trapping as the thin layer of metal resists fusing for a short period of time after the glass is plastic.</p>
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<p>Thanks for your tips when we were first getting started.</p>
<p><br/> <br/> <cite>KarenB said:</cite></p>
<blockquote cite="http://cone6pots.ning.com/forum/topics/warm-glass?commentId=2103784%3AComment%3A130650&xg_source=activity#2103784Comment130945"><div><p>Norm, <br/><br/>><span>The fact that Bullseye glass likes to be 6.8 mm thick is pretty clear, so we'll be using 3 mm sheets for most projects.<br/></span><br/>It's not just Bullseye glass that wants to be 6mm thick.<br/>Bullseye glass is great, I personally am fond of Uroboros, but have used both.<br/><br/>><span>When do you need to add the borax (aka Devit Spray) to maintain a clear glass surface?</span><br/><br/>Devit is applied before fuse firing.<br/>Here's a great link to info about devitrification and how to avoid it. <br/><a rel="nofollow" href="http://www.clearwaterglass.com/Tutorials/Devitrification.html" target="_blank">http://www.clearwaterglass.com/Tutorials/Devitrification.html</a><br/>It's very important that the glass is super clean before firing. No fingerprints. <br/>And that your kiln is clean, the atmosphere inside can cause devit too.<br/><br/>Just to clarify - there's really no reason you can'/shouldn't use a ceramic kiln for glass. <br/>It's just that glass kilns usually have a lower temp range and they often have elements in the lid which helps to heat evenly. A drawback being that kiln bits from the lid can sometimes fall onto the glass pieces and ruin them. <br/>I use a Skutt kiln that is actually a ceramic kiln, no elements in the lid and it works just fine with a fairly slow ramp. <br/><br/>><span>I'm quickly seeing how it might be even better to work with Billets - the 5" x 10" x 3/4" pieces.</span><br/><br/>I have not tried this, but, it seems you could get some great results by fusing some billets together (edge to edge) to form a larger than 5"x10" thick sheet, then slump it into your mold. <br/>When fusing you would need to use a dam to keep the 3/4" thickness which is basically done by building a "container" on the perimeter to hold the glass' outer edge from spreading. This can be done by using kiln shelf stilts horizontally on the shelf and lining the edge with kiln shelf paper (made for glass). You would need to be sure the perimeter is heavy enough (adding a second 'reinforcement perimeter is a good idea) to keep the glass from spreading and that it meets the kiln shelf squarely, otherwise the glass is likely to ooze a bit at the bottom. <br/><br/>Regarding bubbles, long soak is one way to reduce bubbles.<br/><br/>><span>limits to the plasticity of the glass, where the glass sheet separates into several pieces if the angle of the form is too great, which may mean I need to lower the temperature of the pre-programmed firings, rather than change the shape of the mold.</span><br/><br/>I would agree, lowering the temp would be a good idea. You don't need full fuse temp in order to slump into a mold.<br/><br/>Hope this helps!<br/><br/><br/><br/></p>
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</blockquote> The argon/CO2 is mostly inert…tag:cone6pots.ning.com,2016-05-08:2103784:Comment:1308472016-05-08T03:28:03.128ZRobert Coylehttps://cone6pots.ning.com/profile/RobertCoyle
<p>The argon/CO2 is mostly inert gas... It is NOT either and oxidizing or a reducing atmosphere. It inhibited any sort of surface chemical reaction from taking place. So metals do not take on an oxidation layer. Or if you had an already oxidized metal... say CuO, it would not reduce it down to Cu metal. Nor would it remove the oxidation layer off of your kiln elements. </p>
<p>So ( in theory) you could have shiny copper, or silver metal fused into the glass Without causing discoloration due to …</p>
<p>The argon/CO2 is mostly inert gas... It is NOT either and oxidizing or a reducing atmosphere. It inhibited any sort of surface chemical reaction from taking place. So metals do not take on an oxidation layer. Or if you had an already oxidized metal... say CuO, it would not reduce it down to Cu metal. Nor would it remove the oxidation layer off of your kiln elements. </p>
<p>So ( in theory) you could have shiny copper, or silver metal fused into the glass Without causing discoloration due to the creation of soluble oxides in the presence of air... or have a stainless steel inside mold that would not leave an oxidation ring on the slumped glass.</p>
<p>This is all "theory" Karen, and until some body tries it, it remains such. As a chemist, I ran a good number if reactions under Argon gas to prevent oxidation, but in a much more controlled environment and at much lower temperatures.</p>
<p></p> Thanks for the great technica…tag:cone6pots.ning.com,2016-05-08:2103784:Comment:1307492016-05-08T00:46:24.021ZKarenBhttps://cone6pots.ning.com/profile/KarenB
<p>Thanks for the great technical info guys!<br/>Way beyond my chemical knowledge.... but very interesting!<br/><br/>Robert:<br/>Would you be willing to help me understand how that would be different than firing in reduction?</p>
<p>Thanks for the great technical info guys!<br/>Way beyond my chemical knowledge.... but very interesting!<br/><br/>Robert:<br/>Would you be willing to help me understand how that would be different than firing in reduction?</p> Since I also do mig welding,…tag:cone6pots.ning.com,2016-05-07:2103784:Comment:1306522016-05-07T22:42:44.530ZRobert Coylehttps://cone6pots.ning.com/profile/RobertCoyle
<p>Since I also do mig welding, I have often thought of the trouble it would eliminate if I were to seal my kiln a little better and introduce argon/CO2 during the run. All you would need is enough to displace the air throughout the run. Not much really.</p>
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<p>I will do this down the line, as I do see it as a viable approach, especially as I would like to incorporate metal into the clay sculpture.</p>
<p></p>
<p>Anyway, this probably would help the oxide ring problem.</p>
<p>Since I also do mig welding, I have often thought of the trouble it would eliminate if I were to seal my kiln a little better and introduce argon/CO2 during the run. All you would need is enough to displace the air throughout the run. Not much really.</p>
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<p>I will do this down the line, as I do see it as a viable approach, especially as I would like to incorporate metal into the clay sculpture.</p>
<p></p>
<p>Anyway, this probably would help the oxide ring problem.</p> Thanks. Our glass supplier to…tag:cone6pots.ning.com,2016-05-07:2103784:Comment:1309502016-05-07T21:57:25.086ZNorm Stuarthttps://cone6pots.ning.com/profile/NormStuart
<p>Thanks. Our glass supplier told me we're going to need to "feel our way through the learning process" which seemed sensible advice.</p>
<p></p>
<p>With many failures along the way I'm making only one example of each variation of method and material per firing. Fortunately the low firing temperatures mean firing costs are extremely low, comparable to a gilding firing.</p>
<p></p>
<p>The pre-programmed annealing in our Cress E23 is one hour at 1,000 F and an additional hour at 970 F, while the…</p>
<p>Thanks. Our glass supplier told me we're going to need to "feel our way through the learning process" which seemed sensible advice.</p>
<p></p>
<p>With many failures along the way I'm making only one example of each variation of method and material per firing. Fortunately the low firing temperatures mean firing costs are extremely low, comparable to a gilding firing.</p>
<p></p>
<p>The pre-programmed annealing in our Cress E23 is one hour at 1,000 F and an additional hour at 970 F, while the annealing program for glass beads is eight hours at 960 F. I'll have to find out from Bullseye if these times need to be adjusted for their glass Billets.</p>
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<p>It's interesting to note that the process of <strong>making float glass on molten tin</strong> was first patented in the United States in 1902 and again in 1925. But the process of producing float glass on molten tin was never perfected and used commercially until 1958.</p>
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<p>After millions of Pounds of investment and six years of work by Sir Alastair <strong>Pilkington</strong> and Kenneth Bickerstaff the manufacture of float glass finally became practical.</p>
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<p>The process depends on an atmosphere of 90% nitrogen / 10% hydrogen, with the hydrogen as an oxygen scavenger, to prevent the tin from oxidizing and transferring tin oxide to the glass. In metal, the hydrogen would lead to faults, but it's apparently fine for glass.</p>
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<p>Short of changing the atmosphere of our kiln it seems this transfer of metal oxide to glass greatly limits the use of metal molds to slump glass <strong>over</strong>. My understanding is due to the COE difference glass can only be slumped <strong>into</strong> ceramic.</p>
<p><a target="_self" href="http://storage.ning.com/topology/rest/1.0/file/get/3127174872?profile=original"><img class="align-left" src="http://storage.ning.com/topology/rest/1.0/file/get/3127174872?profile=original" width="288"/></a>So it was interesting to read many reviews of Delphi "glass button molds".</p>
<p></p>
<p>Users were complaining the prongs which form the button holes break after the first use. There may be a solution, but it seems an obvious COE problem upon reflection.</p>
<p></p>
<p>I've read ceramic molds should be repaired with pottery plaster prior to the next use, but it doesn't seem it would be strong enough in this type of mold.</p>
<p></p>
<p>I'd like to try the ZYP type Boron Nitride spray as a release, but the $50 price for a spray can puts me off when a 50 pound bag of calcium carbonate is just $12. For some reason they all use 3% talc in addition to the 97% boron nitride - there must be a reason but I can't think of what it would be.</p>
<p></p>
<p>It's interesting too in the Pilkington Float glass process, the thickness of the glass, after the molten glass flows out of the gate onto the molten tin, is controlled by width restriction of the tin bath and also rotation speed of the gear-toothed wheels which dig into the glass on either side of the tin bed - speeding up to produce thinner glass.</p>
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<p>The float glass process for <strong>very thin and strong</strong> glass for computers and phones relies upon a different glass recipe which naturally flows out to a thickness of less than one millimeter. The "hardening process" of Corning Gorilla Glass floats the glass over molten Potassium, where through ion exchange the much <strong>larger potassium atoms take the place of sodium atoms on the surface of the glass.</strong> These potassium atoms in the surface glass matrix place the glass under a high stress temper without the rapid cooling used to temper Pyrex borosilicate glass.</p>
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<p>The sulfur in the sodium sulfide used in the glass melt apparently acts as a clarifying agent, making metallic impurities transparent and I think does something to help expel bubbles from the glass melt. Manganese and lead seem to act similarly, but sulfur is far less toxic.</p>
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<p><strong>I bought some sodium sulfide to try out in making Cone 6 clear glazes less yellow. </strong> There may be other glass technology concepts as well which could proved useful in glaze making.</p>
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<p>Float glass lines operate 24 hours a day for 16 years or so until the plant is rebuilt.</p>
<p>Quite an amazing process!</p>
<p><iframe src="https://www.youtube.com/embed/ig4G5WbOMLc?wmode=opaque" frameborder="0" height="267" width="475"></iframe>
</p> Excellent point Robert... thi…tag:cone6pots.ning.com,2016-05-07:2103784:Comment:1306502016-05-07T18:56:56.256ZKarenBhttps://cone6pots.ning.com/profile/KarenB
<p>Excellent point Robert... thicker glass annealing is another important factor.<br/>And, Bullseye folks are a great resource!</p>
<p>Excellent point Robert... thicker glass annealing is another important factor.<br/>And, Bullseye folks are a great resource!</p> You have gone far beyond what…tag:cone6pots.ning.com,2016-05-07:2103784:Comment:1306492016-05-07T18:44:33.204ZRobert Coylehttps://cone6pots.ning.com/profile/RobertCoyle
<p>You have gone far beyond what I tried Norm. The people at Bullseye here were very helpful. I think you need some advice from people who have already done some of these things and know about slump time/temperature and annealing time for thicker glass, which becomes very important.</p>
<p>You have gone far beyond what I tried Norm. The people at Bullseye here were very helpful. I think you need some advice from people who have already done some of these things and know about slump time/temperature and annealing time for thicker glass, which becomes very important.</p> Norm, >The fact that Bulls…tag:cone6pots.ning.com,2016-05-07:2103784:Comment:1309452016-05-07T18:20:21.140ZKarenBhttps://cone6pots.ning.com/profile/KarenB
<p>Norm, <br></br><br></br>><span>The fact that Bullseye glass likes to be 6.8 mm thick is pretty clear, so we'll be using 3 mm sheets for most projects.<br></br></span><br></br>It's not just Bullseye glass that wants to be 6mm thick.<br></br>Bullseye glass is great, I personally am fond of Uroboros, but have used both.<br></br><br></br>><span>When do you need to add the borax (aka Devit Spray) to maintain a clear glass surface?</span><br></br><br></br>Devit is applied before fuse firing.<br></br>Here's a great link to info…</p>
<p>Norm, <br/><br/>><span>The fact that Bullseye glass likes to be 6.8 mm thick is pretty clear, so we'll be using 3 mm sheets for most projects.<br/></span><br/>It's not just Bullseye glass that wants to be 6mm thick.<br/>Bullseye glass is great, I personally am fond of Uroboros, but have used both.<br/><br/>><span>When do you need to add the borax (aka Devit Spray) to maintain a clear glass surface?</span><br/><br/>Devit is applied before fuse firing.<br/>Here's a great link to info about devitrification and how to avoid it. <br/><a href="http://www.clearwaterglass.com/Tutorials/Devitrification.html" target="_blank">http://www.clearwaterglass.com/Tutorials/Devitrification.html</a><br/>It's very important that the glass is super clean before firing. No fingerprints. <br/>And that your kiln is clean, the atmosphere inside can cause devit too.<br/><br/>Just to clarify - there's really no reason you can'/shouldn't use a ceramic kiln for glass. <br/>It's just that glass kilns usually have a lower temp range and they often have elements in the lid which helps to heat evenly. A drawback being that kiln bits from the lid can sometimes fall onto the glass pieces and ruin them. <br/>I use a Skutt kiln that is actually a ceramic kiln, no elements in the lid and it works just fine with a fairly slow ramp. <br/><br/>><span>I'm quickly seeing how it might be even better to work with Billets - the 5" x 10" x 3/4" pieces.</span><br/><br/>I have not tried this, but, it seems you could get some great results by fusing some billets together (edge to edge) to form a larger than 5"x10" thick sheet, then slump it into your mold. <br/>When fusing you would need to use a dam to keep the 3/4" thickness which is basically done by building a "container" on the perimeter to hold the glass' outer edge from spreading. This can be done by using kiln shelf stilts horizontally on the shelf and lining the edge with kiln shelf paper (made for glass). You would need to be sure the perimeter is heavy enough (adding a second 'reinforcement perimeter is a good idea) to keep the glass from spreading and that it meets the kiln shelf squarely, otherwise the glass is likely to ooze a bit at the bottom. <br/><br/>Regarding bubbles, long soak is one way to reduce bubbles.<br/><br/>><span>limits to the plasticity of the glass, where the glass sheet separates into several pieces if the angle of the form is too great, which may mean I need to lower the temperature of the pre-programmed firings, rather than change the shape of the mold.</span><br/><br/>I would agree, lowering the temp would be a good idea. You don't need full fuse temp in order to slump into a mold.<br/><br/>Hope this helps!<br/><br/><br/><br/></p> Thank you Karen and Robert. …tag:cone6pots.ning.com,2016-05-07:2103784:Comment:1305902016-05-07T07:23:37.367ZNorm Stuarthttps://cone6pots.ning.com/profile/NormStuart
<p>Thank you Karen and Robert. I've lots of questions.</p>
<p></p>
<p>When do you need to add the borax (aka Devit Spray) to maintain a clear glass surface?</p>
<p></p>
<p>I already discovered the metal oxide transfer, even with kiln wash.</p>
<p>I've used commercial glass wash, which I'm told is 2/3 kaolin and 1/3 pottery plaster.</p>
<p></p>
<p>I've also used calcium carbonate which is more work but seems to provide a smoother surface.</p>
<p>I use white wash (calcium hydroxide) on the shelf…</p>
<p>Thank you Karen and Robert. I've lots of questions.</p>
<p></p>
<p>When do you need to add the borax (aka Devit Spray) to maintain a clear glass surface?</p>
<p></p>
<p>I already discovered the metal oxide transfer, even with kiln wash.</p>
<p>I've used commercial glass wash, which I'm told is 2/3 kaolin and 1/3 pottery plaster.</p>
<p></p>
<p>I've also used calcium carbonate which is more work but seems to provide a smoother surface.</p>
<p>I use white wash (calcium hydroxide) on the shelf to provide a base layer, then apply whiting mixed with water with a plastic rib to a super-smooth surface. With some initial application like the white wash, the calcium carbonate really doesn't like to adhere to cordeirite shelves.</p>
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<p>The fact that Bullseye glass likes to be 6.8 mm thick is pretty clear, so we'll be using 3 mm sheets for most projects.</p>
<p></p>
<p>Personally I wanted to try using nuggets / pebbles to makes a bowl more like this one on the cover of this book, but in reading the description it mentions "<strong>cold working</strong>" which I assume must mean a lot of grinding which we're not set-up for.</p>
<p></p>
<p>I understand in concept larger "nuggets" will create fewer bubbles than frit or smaller glass pieces, but I'm quickly seeing how it might be even better to work with Billets - the 5" x 10" x 3/4" pieces.</p>
<p><a target="_self" href="http://storage.ning.com/topology/rest/1.0/file/get/3127174965?profile=original"><img class="align-left" src="http://storage.ning.com/topology/rest/1.0/file/get/3127174965?profile=original" width="383"/></a></p>
<p><strong>So in theory I suppose something like this bowl to the left is made by</strong> placing the glass (billet or nuggets) into a ceramic bowl and forming the interior, necessarily due to the COE, with a piece of metal weighted down so it doesn't float on the molten glass. Finally grind off the metal oxidation transfer, and polish?</p>
<p>Unless someone can think of a more direct method.</p>
<p>In my imagination I assume firing the glass to a temperature above the typical 1,450 fusing temperature would lower the glass viscosity and help any bubbles to migrate up and out of the glass. But it's perhaps likely the glass might bond to the ceramic at higher temperatures like 1,900 or so, and certainly start to incorporate the kiln wash rather than be separate from it - something to try for sure, unless someone else here has already.</p>
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<p>In making my own slump molds for 6 mm glass sheets, I'm also discovering there's limits to the plasticity of the glass, where the glass sheet separates into several pieces if the angle of the form is too great, which may mean I need to lower the temperature of the pre-programmed firings, rather than change the shape of the mold.</p> The dark ring was due to oxid…tag:cone6pots.ning.com,2016-05-07:2103784:Comment:1303602016-05-07T01:03:46.391ZRobert Coylehttps://cone6pots.ning.com/profile/RobertCoyle
<p>The dark ring was due to oxidation of the stainless steel. Even stainless will oxidize at slump temperatures and leave an iron oxide ring on the inside where it touches the glass. Tried coating the top edge with kiln wash or a wrap of kiln paper, worked pretty good but still happened some times. Tried sanding back down to metal...this also helped.</p>
<p>I did not get too involved in this for long, since we were just seeing what we could do with glass without too much expense, in the…</p>
<p>The dark ring was due to oxidation of the stainless steel. Even stainless will oxidize at slump temperatures and leave an iron oxide ring on the inside where it touches the glass. Tried coating the top edge with kiln wash or a wrap of kiln paper, worked pretty good but still happened some times. Tried sanding back down to metal...this also helped.</p>
<p>I did not get too involved in this for long, since we were just seeing what we could do with glass without too much expense, in the existing ceramic kiln. Made some slumped glass candle holders for sale at the local senior center using this method. Not a big problem since the candle covered most of the bottom where the ring was.</p>
<p></p>