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Glass blowing


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Recently I stumbled upon a youtube channel with loads of amazing glass blowing videos and I've probably spent a few hours glued to my screen drooling over the videos, so I of course started thinking about doing this myself, has anyone used a propane forge with Frosty's T burners for glass blowing? are there any reasons why that wouldn't work?, my biggest concern is it might be too hot

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As a former professional glass blower I have to say I got a bit of a laugh out of this, no insult intended. 

Of course you can use a NA burner like Frosty's for glass blowing, and a propane forge will work just fine as a glory hole (in fact the ones I've used pretty much just looked like larger versions of what you would see as propane forges.  Unfortunately that is just one half of the glass blowing equation as regards heating glass (reheating).  The more important side is the furnace that melts the glass from either batch (dry materials) or cullet (pre-melted glass that gets broken back into shards then re-melted). This furnace needs to withstand very high temperatures and a very corrosive atmosphere (imagine a high alumina refractory crucible full of molten flux for example).  Corning uses platinum lined furnaces to melt their high end leaded glass, but the rest of us make do with lesser cost/quality glass contact liners. It also, due to the nature of the refractory, needs to heat up and cool down very slowly, as cracks in the refractory can destroy the furnace.  For that matter you pretty much require a computer controlled annealer to slowly cool the glass after production, as it is also subject to thermal shock if it just air cools (want to see more cool videos, look into glass Prince Rupert drops).

I can carry on for hours regarding glass equipment design, and I'm sure it is more than you want to hear.  The learning curve for glass blowing is also quite steep.  Having done a  bit of both at this point, I would say it is even tougher than smithing to pick up.  I suggest you try it at an established facility before going out to set up for yourself.

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I've got a question for you. What is a good release agent to prevent glass fro sticking to what you don't want it to. I swear molten glass has to be one of the stickiest stringiest things I've ever seen. Beats sticky spider silk all hollow.

Frosty The Lucky.

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Molten glass won't stick to anything appreciably cooler than it is, but that will also lead to the glass cracking due to cooling on contact.  I probably need to know more about the process you are planning on.  If you are thinking of casting molten glass into a metal mold, a lot will depend on the relative temperatures of the two materials as well as the different thermal expansion ratios.  Timing also plays a role.  I've cast molten glass into sand, wood, aluminum, brass, plaster and graphite molds, but it needs to be removed from these at just the right time (set to rigidity, but not cooled down too far) and then put in a temperature controlled chamber to get annealed.

To achieve clean castings (into say sand or plaster molds) I've often used a layer of carbon deposited on the surface.  We used to either put on a layer of lamp black using an acetylene torch (which also preheated the mold), or used spray on powdered graphite.  The carbon works well as a release and can easily be cleaned off the glass surface.  I was using soda/lime/silica glass (hard glass) as opposed to borosilicate (Pyrex, soft glass) so that is also an issue.  Different glass compositions behave just as randomly as different grades of steel.

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What I was doing is filling the negative space in a spread cross with red lampwork noodle and later red frit. 

I wanted a little flow flow than slump. Below is one of the more successful noodle crosses. 

The second pic is with frit as the glass. It's also one of my bottle openers though I don't know what I was thinking making it twist to open bottles. <sigh>

I figured the frit wouldn't need to become as liquid to fill all the nooks in the negative space. Keeping it IN the negative space turned out to  be the real challenge, the stuff wicks rought out between the back of the cross and whatever it's resting on. This is a soapstone tile and the back of the cross is almost enameled in red glass.

I made up a clamp with a flattened SS spoon bending the handle around as a clip. No joy.

I picked up a refractory paper specifically for working with glass and tried that as gasket material under the cross. Again no joy, stuck to that too. A piece is the white square on the tile.

Gently bedding it in high alumina refractory pretty much glued the cross to the refractory. Surprised?

I believe I can get this to work IF I can keep the glass from sticking to the backer.

I've had good success annealing by leaving the piece to cool in the chamber next to the one in the forge I used to slump the glass. Leaving it in the HOT chamber to anneal wasn't desirable, the forge floor was covered in red glass. Oh and I've already been told this can't be done by owners of art glass supply shops who couldn't get it through their heads I was putting the glass in the steel cross not the cross in a piece of glass even after showing them the one in my hand. I gave up trying to explain to them.

My experience has been once the glass softens it gets on everything, glass fibers almost spontaneously fling themselves out of the project to stick to the forge, tools, me the anvil, spread around the floor. every DARNED thing within about 8' has glass fibers stuck to it.

So, how much am I doing wrong?

Frosty The Lucky.


58f6b2febef68_Splitcrossredglass.thumb.JPG.bee2a5c0b6a0a102990dec2a24b7bcf1.JPG 58f6b411c085e_carvedsstoneback.JPG.361dc59a913ed740897427bb0c4e84d3.JPG

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The lamp worked glass you are using is most likely borosilicate glass, which I have admittedly less experience with.  On the plus side it has a much more forgiving (larger) working range and if I recall correctly it's thermal expansion ration is closer to that of metal.  However, in my experience, fusing glass into steel sets up stress conditions that are potentially an issue, if not immediately then down the road.  If the glass was clear, then use of a crude polariscope can show this easily, but with colored glass I think you are in trouble.

Glass is subject to thermal shock from both cooling quickly and heating quickly, primarily due to its brittleness and status as an insulative material (the outer skin of glass heats or cools more quickly than the interior, which sets up stress conditions sometimes leading to fracture).  This is what you experienced when you put the glass into the forge and it exploded and flung itself everywhere in your shop.  The only way to avoid this is to either enclose the glass in a container while heating or heat it up very slowly.  Molten glass is basically the same thing as molten flux, so it will eat away at your unprotected forge interior as well.

Not sure why the sheet refractory paper didn't work as a resist for you.  You may have gotten the glass too hot.  I have used that paper, and refractory board, in the past to slump glass over, but there the glass only goes up to around 1200 deg where it starts to fuse and deform, but does not go to liquid state.

If I were doing this project I would use the following steps:

  1. Switch to copper for the cross (better thermal compatibility with glass, but not perfect, so must be tested - consider enameling frit instead of lampworking)
  2. Punch the "heart" location partially through the copper stock, so there is a depression that can be filled with glass rather than a hole
  3. Slowly heat the assembly in an electric heat treat oven (ideal), enameling kiln (fair) or gas forge at a very low candle to about 1400 deg. F (depends on type of glass, borosilicate frit may fuse at a lower temperature)
  4. Hold at the fusing temperature for  around 15 minutes.
  5. Rapidly reduce the temperature to between 875 and 925 degrees (annealing temperature, again depends on the glass).  Note that the rapid reduction here is to limit devitrification (kind of like decarburization in high carbon steel, but more visual).
  6. Hold at that temperature for at least an hour.
  7. slowly cool down from the annealing temperature to around 300 degrees (by slowly I mean no more than 50 degrees per hour, this is where a programmable oven shines)
  8. crack open the enclosure and let it cool to room temperature.

Good luck

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