I accidentally knocked a decanter off of a shelf in the garage. As I was sweeping the pieces up I got to wondering about melting it down and pouring it. How would one go about doing that? What type of casting would you use? If this has a better location in the forum then please move it there, I couldn't figure out where to post it.
I think much of the glassware we see that has an obvious parting line was made by blowing a blob of glass within a mold. https://en.wikipedia.org/wiki/Early_American_molded_glass There is also a process call slump molding. I do not think glass flows very well for actual typical molding like that done for many metals. Denis
I dont know much about glass but I've come across a couple pictures looking up "sand casting", of glass being cast in sand molds. IIRC from what I saw open molds were used, no skinny tapered sprues here. Jeff
Glass doesn't have a discrete melting point the way that metals do instead, glass softens with heat, the hotter it gets, the softer it gets but it never gets fluid enough to properly fill a mold unless it's put under pressure.
Glass is very plastic and can be a royal pain in the ass. If you want to cast glass, you must have at a minimum a PID controlled kiln with ramp and soak capability. It's very similar to lost wax casting. Be warned, it does require specific glass, lots of trial and error and do not expect a shiny finish without massive amounts of cold working. If you want to cast glass into a mold, it just requires heat and time. With the right investment material, it can be melted into about any shape req'd. Pressure is not required for solid objects. Here is a very long and boring thread about some of my adventures casting glass. http://forums.thehomefoundry.org/index.php?threads/chunk-jewel-lamp.622/ I have successfully done it using R&R bandust 101 investment. It's cheap, but one time use only. If you want to heat glass and press into a mold, graphite is the answer. After the shape is attained, you must hold at anneal and then go slow through strain temps. Like I said, it can be a pain in the ass. Your decanter is toast, throw it out unless you know for sure it's real lead crystal. That's the best kind of glass for casting. Shit like beer bottles and common crap from goodwill is a no go. KNOWING the COE of your glass is really key to the piece surviving. To make things even more tricky, if you mix glass of different COE; YOU'RE HUMPED! (Coefficient of expansion)
I've been a glass fuser for over 25 years; glass is heated in a kiln to "fuse" the individual elements into one solid piece. Fusing temps vary between 1400 for "tack fuse" and 1500 for a "full fuse" which results in a completely flat surface. In it's molten state, glass is self-leveling and seeks a height of 1/4". You can melt glass together to result in greater thicknesses, but you must "dam it up" by creating a reservoir and lining it with a refractory material so that it won't stick. I build my dams from soft brick and use 1/4" refractory blanket as the liner - be advised that coldworking is necessary to remove the bits of refractory - I have both a 20" diameter flat lapper and a 7' h vertical belt sander - these tools will cut your cleanup time by 90%, but you still will need to move through the various grits of sandpaper if you want a shiny finish. An easy way to "play with casting" is to get a clay flower pot with a hole in the bottom, and fill it with glass. As mentioned previously, you cannot just throw "any glass" into the pot - it must all have the same COE - coefficient of expansion - or it will crack once it has cooled. Since the broken decanter mentioned above was from a single item, I would guess that it could be successfully melted using the flower pot method. To cast this way, you need a kiln that will accommodate both your mold and the flower pot, which is suspended directly above the mold (the mold must be coated with kiln wash, which acts as a mold release... there will still be coldworking needed. Successfully working in "hot glass" requires a knowledge of "ramp times" (both up and down) - how quickly you heat up/cool down the glass, as well as annealing time (dependent on thickness and surface area of the glass), and the strain point. Metal is far more forgiving in this respect. If anyone wants more info on glass casting, this link is a good resource for glass casting using the lost wax method http://www.castglassforms.com/ One of my favorite glass caster is the Swedish artist, Bertil Vallien https://www.kostaboda-artgallery.com/artist/bertil-vallien
Great video.... I have never seen a polisher that "vibrates"... that certainly reduces the coldworking! Something similar is in the was they polish flat slabs of granite for use in countertops....running water moving back and forth over the surface... all automated. The amount of time needed in the kiln was both for annealing the very thick glass, as well as letting it sit at the bottom of the ramp, so that the molecules could stabilize - one must take into account ambient air temperature outside of the kiln, once you open the lid. Since the kiln retains heat, letting a piece sit inside until everything is completely cool is imperative, as glass does not allow for a "second chance".... I am familiar with the "ping" of trying to rush a piece out of the kiln.... but you learn fast, given the amount of time that goes into the project.
I live about 50 miles from the Pilchuk Glass School started by Dale Chilhuly. It is an absolutely amazing center stuck in the woods whose sole purpose is to push the limits of learning and glass art-making. I have visited twice when they offer a day once a year open to the "unwashed" ignorati of glass --- I am a charter member of the ignorati. ;-) If you want to learn about glass, that would be a good place to spend a year or two. Denis
I'm more of a metal guy, it was just a passing thought as I was looking at the broken glass on my garage floor.
I often wonder if working potassium glass would save most of the grief of quick cooling: the stuff has much less internal stress compared to sodium glass and much less tendency to crack.
Glass artists regard visiting Pilchuk as a once-in-a-lifetime pilgrimage... I've yet to make it there.
I had the good fortune of seeing the Chihuly exhibition at the Albright Knox Art Gallery in Buffalo about 20 years ago. My girlfriend at the time was a professional sculptor and I got introduced to an awful lot that I would have otherwise never seen. Pete
I saw his exhibit at the Dallas arboretum about 10 years ago. He's quite the artist. Of course saw his display in the Bellagio last time I was in Vegas
One interesting factoid regarding the explosion the art glass movement is related to the development of the small furnace which has freed glass workers to work solo or in very small groups. Prior to development of the small glass furnace glass work was necessarily confined to large operations supporting a large furnace and a sizable workforce needed to efficiently use these furnaces. Art glass as such was a relative rarity prior to the 60’s. From Wiki: “Recent developments[edit] The "studio glass movement" began in 1962 when Harvey Littleton, a ceramics professor, and Dominick Labino, a chemist and engineer, held two workshops at the Toledo Museum of Art, during which they started experimenting with melting glass in a small furnace and creating blown glass art. Littleton promoted the use of small furnaces in individual artists studios.[34] This approach to glassblowing blossomed into a worldwide movement, producing such flamboyant and prolific artists as Dale Chihuly, Dante Marioni, Fritz Driesbach and Marvin Lipofsky as well as chronicglass and scores of other modern glass artists. Today there are many different institutions around the world that offer glassmaking resources for training and sharing equipment. Working with large or complex pieces requires a team of several glassworkers, in a complex choreography of precisely timed movements. This practical requirement has encouraged collaboration among glass artists, in both semi-permanent and temporary working groups.” Denis
