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Author Topic: Melting glass  (Read 20581 times)
sidecar_jon
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« on: February 04, 2011, 06:24:40 pm »

Ok so a strange one, but i bet some one here knows what's what. I've been endeavouring to make glass blobs, but melted into round copper pipe sections. In the spirit of experimentation i've been using old rough glass beads,(i think African made from old beer bottles) which when heated explode! But after they have done that, they melt quite well. However they do discolour with direct torch application. Anyone know anything about glass and its melting using low tech techniques?
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Captain Shipton Bellinger
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« Reply #1 on: February 04, 2011, 08:02:27 pm »

Glass beads are generally wound on to a mandrel from a stick of melted glass. As it cools stress planes can become fixed in the glass, which is why they explode on reheating, especially if you bring it into the flame too quickly. I've had this happen a few times when I think "I'll just true this bead up a bit more...". If you introduce the heat more gradually you may get away without that PING!

Not sure why your glass should discolour so noticeably, but it could be that the pigment is oxidising at the temperatures you're using, or that the combustion products of the gas itself are reacting with the pigment. I recommend using MAPP gas for glass work - it burns hotter than butane/propane and, more importantly, has a much cleaner flame.



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sidecar_jon
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« Reply #2 on: February 04, 2011, 08:55:28 pm »

I might be overheating it, a big propane torch is hardly the most delicate thing. I hope to arrange an underneath heating system. Are they not "tempered"? I've seen the local glass blower making things and his bowls get  24 hours in an over after completion...
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Mr. Boltneck
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« Reply #3 on: February 05, 2011, 12:36:33 am »

I don't know a huge amount about glass myself, but people I know who work with it tend to anneal it in a kiln. I have also heard that for beads, some vermiculite or sand in a metal bowl on a hotplate can be used. The idea is to cool the beads slowly enough that stresses do not build up due to rapid cooling—the inverse process of the rapid heating which is making your beads explode. Also, color in glass and ceramics is frankly weird. If you've ever worked around glazes and frits, you'll see all sorts of color changes, which can vary with time and temperature of firing.
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torkbox
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« Reply #4 on: February 05, 2011, 03:43:09 pm »

Melting is easy, it's cooling it down without cracks that's tough. For small bead-sized chunks though I think you can use your home oven to slow the cooling down and prevent this. I'd check a lampwork forum or DIY article for that.
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dingbat
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« Reply #5 on: February 05, 2011, 05:10:26 pm »

You need a kiln to work with glass. You might use a very rough and ready kiln, but you do need a kiln.  Anything like a bare torch flame in the open air will cool down far too fast once the heat is off.

A problem with glass is it cracking _after_ it's cold - maybe weeks afterwards. Glass doesn't crack because it's cooled too fast, it gets internal stresses if you cool it unevenly or too fast, and these stresses are in turn what causes the cracking. The stress to crack interval can be very long, and is often triggered by some outside impact. So making "safe" (let alone reliable) glass depends on your process being well enough under control that you can rely on it to not leave you with stressed glass, even if it didn't crack immediately.

Kilns need firebricks. You need to hold temperatures of 300-400 Celsius and also 500-600 Celsius for quite some time, and also to reach temperatures of 700-800 Celsius briefly for working. This is way beyond domestic ovens or anything made of metal, rather than firebrick. However it's less than most ceramic kilns, so it's a bit easier than that.

For jewellery scale work, a front-loading electric kiln of about 4" square, is useful and not too awkward to find space for. Not dreadfully expensive either, as there are many around S/H. A PID temperature control and SSR is £35 from China via eBay and well worth it, although not essential, especially at these small sizes. A thermocouple pyrometer is pretty much essential though.

Next size up is a kiln a bit like ours (a Skutt Firebox) which is an 8" square top-loader. These can make plates and dishes, and might use a cycle time of up to six hours, where automation does become very useful, just for the convenience. It will also handle small jobs quickly though. Above that are clamshell box kilns which cost £1000 and upwards. They also take longer to warm up, even for small jobs.

I can't see the justification of home-built glass kilns working out, unless you either have most of the materials to hand already, you have no budget to buy one, or you're building something large and specialist. Otherwise the S/H route is the best access to getting the lowest cost kiln for a reasonable cost and effort. If you have courses nearby (most glass retailers also run courses), these can be a very useful route to accessing a kiln. It's also a good way for someone with a little experience with a small home kiln to rent time in a big kiln for special projects.

Glass is best bought from a specialist decorative glass supplier, and all of one brand (I use Bullseye for hot working - try Warm Glass in the UK). The reason is their differing coefficients of expansion, so mixing glass from different ranges is problematic and usually unrewarding long term. If you're only working one glass though, you can use something far cheaper - often recycled. Our Christmas cards were slumped from cheap greenhouse glass, with tiny spots of Bullseye fused onto them. I expect a couple might shed their baubles in months to come, but sic transit gloria mundi. Frit casting (granulated glass fired in moulds) can be fun, and it's a great way to use coloured glass bottles, or even damaged ornaments. The truly brave rework uranium glass (my nocturnal sundial project).

For more advice (glass behaviour at temperature is complicated!), my favourite starter book is Beveridge's Warm Glass.
« Last Edit: February 05, 2011, 05:13:17 pm by dingbat » Logged
torkbox
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« Reply #6 on: February 05, 2011, 05:42:35 pm »


You need a kiln to work with glass.



Hold on a second.....my brain re-engaged!

At the various fairs, faires, & carnivals here I recall there is usually someone with a booth making glass animals like the ones below. They have an adjustable gas torch that can make either soft flame or focused one. IIRC, they build up the animal from glass rod and keep adding it until it is a size they want. Sometimes they get to nearly 25mm in cross-section. After they finish with the design, they hold it in the soft flame briefly and set off to the side until it cools, in open air. When it is cool to the touch they hand it to the person who bought it. This is anything but a controlled process and I believe it is a perfect example of "lamp"work.

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sidecar_jon
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« Reply #7 on: February 05, 2011, 06:10:29 pm »

thanks for the useful advice. I wasn't really thinking of a kiln set up for what i need but i have seen single brick type propane torch kilns etc, which i might have to make. That's if i cant work out how i did it last time!..
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dingbat
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« Reply #8 on: February 05, 2011, 06:35:33 pm »

Lampwork sometimes uses a "cooling can" rather than a kiln as such. This is a tin can filling with an insulating material that doesn't stick - usually Perlite (Vermiculite can shed dust). Wood ash works well too, but tends to stick dust into the surface. Sand and most minerals are useless, as the're too dense and thermally conductive.

Fairground lampwork is infamous for cracking a week after sale, because it was cooled too quickly (and often used incompatible glass). Wings crack off birds etc. If it's done with more care and the can is used for cooling rather than open air, then it should be more stable. Mostly though, this sort of small lampwork survives precisely because it's small, and thus mechanically less susceptible to the same level of stress.

Beadworkers use a similar cooling can too, although most semi-commercial beadmakers looking to make a reliable product will use an annealing kiln. For beadwork these are front loaded, usually through a small "letterbox" flap, so that beads can continually be placed inside without opening the main door and losing too much heat.
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torkbox
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« Reply #9 on: February 05, 2011, 06:43:04 pm »


Fairground lampwork is infamous for cracking a week after sale,

Perhaps, but.... somewhere I've got a duck from 30 years ago that kept itself intact, not inbits. The mouse my son bought for his sister several years back has not either.

I doubt we are unique in our sans crack good fortune.

 Wink
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sidecar_jon
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« Reply #10 on: February 05, 2011, 07:48:49 pm »

Currently i'm trying to make a brooch similar to one i made for the wife a year or so back. The original isn't perfect but its way better than i can achieve now. I think i painted water on copper dusted the glass powder on, heated and sprinkled clear on it when red hot, however shiny copper is amazingly water resistant. I think i used Borax flux somewhere along the line , but the winning combination eludes me at present.
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dingbat
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« Reply #11 on: February 05, 2011, 08:03:35 pm »

OK then, that's enamel rather than glass. Although it's still "glass", it's not chemically the same as most glasses you'd handle as flat sheet and most importantly it's a very thin layer of glass on a thick piece of copper.

It works best in a kiln, but it works fine with most torches. Use a large "bushy" flame so that it's even heating. The best way to work is to have some stainless barbecue mesh projecting out from your hot bench, place the copper piece onto that, and heat from beneath. Don't heat it cold from above, or you blow the enamel away. Don't heat it hot from above, or flame chemistry can mess with your colours. To cool it, just leave it on the mesh and let it do its own thing for a few minutes. So long as it isn't draughty, it'll be fine. When it's cool enough to handle, pickle it (acid clean to take the fire scale off the copper). The one thing not to do is to pickle it hot, because that really will crack the enamel off the metal.

If you're counter-enamelling (enamelling both sides), then that really does need a kiln.
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sidecar_jon
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« Reply #12 on: February 05, 2011, 08:26:43 pm »

ah yes.. i'm making enamelled brooches and glass blob in copper things...sort of separate but similar things. Cheers for all the advice. My powdered enamels are off an indeterminate type and composition, just a gift of odd colours, i don't even know the make etc, so experimentation is the order of the day.. cheers again.
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hardlec
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« Reply #13 on: February 08, 2011, 03:29:04 am »

Lamp-work is very tricky.  I tried it several times, and had modest success.  It is very easy to make a bead that will shatter from a moth's wing touch a month after it was made, and possible but unlikely a piece will last a long time. 
doing Cloisonne, enamel, or slumping glass, well, I'd recommend a kiln AND some study time with a master.
To do lamp-work, you need the proper tools and time with a master.  The Carny lamp-worker is probably not a good choice. I am not either.
Glass blowers use the "glory hole" a furnace, which has very precise temperature control.

A few months ago, I took some seed-beads, crushed them to a fine powder, then used a micro-torch to heat some powder to liquid.  The liquid formed a ball.  I made sufficient balls of various sizes to make eyes for a 25mm monster. I made about 20 examples to get 6 pieces I liked for the eyes I needed (yes, the monster had 6 eyes.  You gotta problem wid dat?)

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dingbat
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« Reply #14 on: February 08, 2011, 01:38:58 pm »

The only lamp work I've done was a course in making lab glassware. The funny thing is that because we were using borosilicate glass, i.e. Pyrex (generally an utter pain to work with), the cooling issue becomes so much easier (because the glass is just so much less sensitive) that we didn't even consider it. However something as simple as cutting tube becomes difficult, in comparison.
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heavyporker
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« Reply #15 on: March 20, 2011, 10:10:52 pm »

I'm impressed by your efforts on this thread, Mr. Dingbat. Do you do lamp work or that lab glasswork professionally? About these small kilns like the Skutt.. Firebox, what is the general price range one should expect to see for these? Are they expensive? I'm considering going into glass lamp-work and I like reading up on the details so I have some idea of the general picture. Thanks for the help you've given so far, Mr. Dingbat.
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dingbat
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« Reply #16 on: March 23, 2011, 08:26:05 pm »

My lab glassware course was a long time ago, during my laser physics degree (and you thought I was just playing at the Mad Scientist bit!?)

I'm pretty new to glass and my only commercial involvement with it is small pieces that become embellishments for larger pieces in wood or metal. Just today I fired some cast glass pieces (mixed frit, mostly clear with a little colour in it) into a rectangular slab. When sawn into strips and polished, this becomes material for jewellery.

As to prices, then many of the good kilns (like Skutt) are American and I suspect that I'm suffering from the usual pound=dollar exchange rate and that they'll be cheaper locally. Certainly US prices for art glass like Bullseye and Spectrum are much more attractive than over here. OTOH, we have 240V mains power, so I can run a reasonable kiln from a normal domestic socket and don't need a special circuit for it.

I bought the Firebox 8 because it's small enough to be cheap and fit into the workshop, without being a glassworker's kiln to the exclusion of everything else from the space and budget. It's also the same heating element as their larger kilns, so it fires very quickly and is thus useful for enamelling on copper or silver, or kiln brazing. A bowl-making kiln (12" round) would cost £thousand and probably be a clamshell lid. A 4" front-loader will do jewellery, but not slumped bowls.

With a kiln within easy reach, I now find myself slumping and fusing all sorts of "cheap rubbish" from greenhouse glass at almost no cost. Rather than making a roof for a new birdfeeder from metal or plastic, I slumped one from glass and decorated it with fused stringers. I needed a "porthole" window recently, so I just slumped one up. As it's not a tool I've ever had before, I keep finding new things that I can do with it.
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sidecar_jon
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« Reply #17 on: March 24, 2011, 03:44:08 pm »

I should mention for completeness that i saw a bit on "bang goes the theory" that one can melt glass in a domestic microwave oven. You just need to get the thing hot with a gas torch first. The problem with cold glass is it seem the molecules have no room to move so you have to get them moving with heat first.... is this how they make them melted coke bottle fairground novelties?
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Winny
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« Reply #18 on: April 18, 2011, 12:44:29 am »

Ok this is where I place my two pence worth, I have a degree in Glass and Ceramics, I am a lamp worker, started off in the late 80's with borosilicate and gold fuming = glass ships in bottles, left it alone for a long while ( life and all that) and now have got back to it. I have a simple propane set up known as a hot head ( due to cost mainly, I will get a big girls torch one day) and I have no kiln, I slowly cool my creations in the end of the flame and place in a slow cooker full of vermiculite to cool completely, then when I have enough  work I take it down to a friendly person who runs a lamp working suppliers known as 'Off Mandrel' and they anneal my work for a fee, its not the best way of doing things and one day I will have a duel fuel torch and my own kiln but thats one day and although this means I can't rush work out it dose mean that any beads  I use or sell are free from the stresses that have been mentions before
If your interested to learn more I may suggest that you goggle a forum called 'Frit Happens', they are mostly harmless and full of information, in fact they have a technical section that I often look at, loads of information on set ups, safety and different techniques
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Videodrome
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« Reply #19 on: May 04, 2011, 04:32:01 am »

I'm not interested in forming new shapes but have wondered about modifying a used Wine bottle into being just a Tube.  Basically getting the ends off one or both sides. 

The idea of trying to cut off the top of a Wine bottle makes me wonder if I would just crack it.  So I wondered if a cutting torch would be more effective. 

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hardlec
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« Reply #20 on: May 24, 2011, 01:38:57 am »

Use a glass cutter.

There are/were kits to re-purpose bottles into tumblers.  They worked, but I usually destroyed one of three bottles.
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