Melting Glass

[Chad J.]

I've been doing the freidrich's cross hummingbirds and just wondered if anyone had tried melting glass and adding it to a piece.  I think that a piece of red glass in the middle of this would look amazing.

[Chad J.]

Just found the glass inlay thread from way back.  Has anyone tried it more recently than 2013?

[BillyBones]

I think Frosty may have done this a time or 2. I seem to recall him talking about how to do it. 

[Frosty]

I've done it more recently than that thread but it's been a while. It's not a complicated process if you're prepared. The biggest problem I had was keeping the glass from sticking to what I was using as a dam on the bottom. The torchwork glass supply carried a paper form of refractory that worked well. Not saying how many tries it took though.

What do you want to do / know Chad?

Frosty The Lucky.

[Chad J.]

I'm looking to melt in different colors of  glass into the opening of my freidrichs hummingbirds.   I think it would be a great touch to make them stand out.  

[Frosty]

I had exactly the same idea for spread crosses but my forge isn't the right tool for slumping glass.

I bought both colored glass "noodles" long flat rods rather than round ones used for glass torch work. And colored "frit", crushed glass, IIRC I bought 40mesh though it comes in other screen sizes (meshes).

What finally convinced me I'd have to take one of the classes so I could use their kilns was temper time. The glass NEEDS a long slow cool down period or it crazes, breaks up or just falls apart. I had marginal successes by firing up the forge and shutting it down when it got a LITTLE hotter than glass likes and then putting the spread cross in and closing it up. On good next mornings there was a cross with a red glass center.

As thick and slow as molten glass flows it seems to penetrate like some demon intent on sticking to everything close. It finds tiny gaps to flow out of. Crazy stuff I can see why folks love to work with it. I would've loved to have discovered it while Chihuli was still teaching.

Anyway, you want the glass to reach slumping temp without actually liquifying and you want to hold it there long enough it fills the voids and fuses. 

I never played with multi colored crosses but your hummer is a perfect place to try.

My thought was a background color frit. Them place cut pieces of colored noodle in the background frit to make patterns. Were I going larger, say a couple inches square I'd try using sand painting techniques but I can imagine tempering would be a mother bear. Colors don't mix or blead unless you mix them but that could be fun. Chihuly was a master at mixing colored glass in clear glass and making the most incredible . . . (pattern is just too weak a term.) Do a web search for "Dale Chihuly glass". I can't find a link to pics without lots of ads for art and artless glass.

I'm not the guy who does torchwork on Iforge, those are the guys to talk to.

Frosty The Lucky.

[George N. M.]

Frosty, a question on your at least marginal technique:  I'll use filling the center of split cross as an example.  I can see heating up the cross and then sprinking frit into the void while the cross is laying on something flat and then putting it back in the forge to melt/slump, then turning off the forge and leaving everything alone until it has cooled down.  My question/fear is how do you keep the glass from sticking to the flat surface on which it is lying.  Do you use some kind of a release agent?

G

[Nobody Special]

I had mixed results slumping marbles into the middle of objects like that. Torches are more accurate but it sometimes seems to have issues if the piece you're slumping it to isn't hot. Glass is finicky - different glasses are finicky different ways.

Iron almost always seems to cause the glass to craze, probably because it has a different coefficient of expansion - copper is surprisingly close, but that would mean the copper would need to be at similar temps. I don't have a kiln, but burying it in ash or perlite with a big heated helper rod to hold heat seems to help...except if it gets too hot, the glass sometimes melts or gets soft and misbehaves again. Have I mentioned glass is finicky? Oh yeah, and if you put it in too hot, sometimes the annealing medium sticks. Seems to be a bit of find the sweet spot for everything and then to try be consistent and lucky.

[Chad J.]

Ok, I went for it.  I used the glass pieces that people throw in the bottom of a fish bowl.   Heated them up in a large spoon I had forged and started warming up the hummingbird.   I had not cleaned the forge scale off yet.  I had the bird at the opening of the forge to start warming it put it on a piece of fire brick on my anvil and started pouring the glass in.   It moved like molasses so before I got it poured I put it back in the forge asking with the bird.   I grabbed a piece of scrap tried again and got it poured and it froze sticking about am inch or so above the bird.  I threw it back in the forge towards the front and let it start falling into place.   I grabbed my flat face punch and used that to push and shape the glass into the opening.   Heated one more time then set it outside to cool naturally.  I'll see if it has any problems overnight but it was cool to the touch when I took these. 

 

BTW Jerry, my girlfriend and I are planning a trip to the Biltmore Estate Gardens to see the Chihuli display in the botanical garden there.  I learned that display travels only to gardens and each location gets a custom made piece that they keep.

[Frosty]

The only thing I found that the glass wouldn't stick to and I could get it cleaned off was the "paper" refractory sold at the glass arts supply where I got the frit and noodles. I filled the negative space in the cross heaping high with frit and "melted" it in the forge near the front and when it started subsiding into the cross shut the forge off and came back in the morning. As high as I heaped glass the negative space in the cross never ended up full. 

I only tried pouring glass once and was cleaning filaments of glass off everydarned thing for some time, I still find one now and then. 

Glass is finicky, indeed. That is why I use torchwork noodles and frit. Every color has it's own traits but the torchwork glass is pretty consistent and requires much shorter temper times. Mild steel and glass have almost identical COEs. Copper's COE is close enough unfortunately it's expansion rate is significantly greater. 

Mild steel not only expands and contracts almost exactly the same temps as glass they move the same distance. Put the glass in the cross (whatever) then bring them to temperature together. In my experience the forge is better than a torch. I don't have a propane torch with a particularly soft flame so I expected problems and got them.

Chad, the only people I know who slumped glass in forgings heated both at the same time like I describe above. Nobody poured it. IIRC the guy at the art glass place said they use polished stainless tools to tamp molten glass. I tried it with a stainless spoon and it worked pretty well, unfortunately it couldn't press the glass into the points in the cross. 

When the frit starts fusing before actually melting, it draws together, a round pile shrinks into a smaller taller circle. If that makes sense. 

Glass and steel seem like they're made to go together HOT. Glass does an excellent job of bonding to steel well enough to be a serious PITA getting off. Worse than clinker sticking to the air grate. 

Frosty The Lucky.

[Latticino]

As you noted, molten glass will stick to red hot steel very nicely, but the difference in thermal expansion coefficients makes it likely that the glass will be under significant stress when the two cool down.  I am most familiar with soda/lime/silica glass (hard glass typically used in "off-hand" glassblowing) rather than borosilicate glass (soft glass used for torchwork.  These have different properties, including thermal expansion and resistance to thermal shock.  All glass melts at different temperatures depending on whether you are melting from raw materials or remelting preformed glass frit (sort of like the difference between smelting and melting iron I guess).  All glass should be carefully cooled in an annealing process to remove the cooling stress it is subject to by virtue of being an insulative material.  You also have to be careful of keeping glass for a long period at elevated temperatures.  I'm not sure what the parameters are for soft glass (though I suspect somewhat higher temperatures are involved), but hard glass will devitrify (lose some transparency) if kept for a long period of time between around 1,000 to 1,500 deg. F.  Annealing is usually slow and controlled cooling from just over 900 deg. F down to around 200 deg. F.  This is usually done overnight in a temperature controlled electric annealing oven.

A couple of notes:

• As mentioned glass thermal expansion coefficients are more compatible with copper than steel for most glasses (I spoke to Al Paley a couple of years ago and he was working with Corning to develop a formula for a glass that would be more compatible with steel for some of his sculptures.  I saw some of the results of this experimentation, but don't know if they ever developed anything that he was happy with).  Retained stress in your embedded marbles would worry me.  Glass under stress that gets scratched or thermal cycled can spall out pretty aggressively.  Research "Prince Rupert Drops" for an interesting example.
• Molten glass will not stick to cold steel at all, though an interesting wrinkled chill mark pattern will form on the rapidly cooling glass.  If the steel surface is thick enough not to get heated to the point where glass will stick, it should work fine to cast against.  Other "resists" for casting glass to use if you want a clean release include graphite spray (make sure no molybdenum in the spray) or just a coating of soot from an acetylene torch.  Float glass is another interesting process where the molten glass was cast onto molten metal (tin or lead) to produce sheets, but I wouldn't recommend that.
• Glass casting from frit is typically termed Pate-de-Verre, from the French.  There are some beautiful examples of this work still being done today. Like casting metal 
• Some glass colors have radically different thermal coefficients and are not compatible with others.  The "hot" colors like opaque red, orange and yellow are often not compatible with the "cool" colors like blue or green.  Glass colors are produced by the addition of metallic oxides to the raw materials during the initial melt.  Some interesting reactions between glass colors can be added by use of silver nitrate or silver bromide powder during remelting, but beware of the fumes.

[Chad J.]

Thanks for all the info guys.   I checked on my piece this morning at it was still intact but I'll attempt tp temper it this evening when I get home.  I'll fire up the forge,  get it to heat and shut it off, putting the piece in there.   It isn't as precise as it probably needs to be but it is what I can do.   I feel like I've opened a whole new can of worms trying this.  I'll have to re-read this all a couple times and see what I want to try and what I don't want to mess with.   I think slumping marbles may be as in depth as I get here.

[mcostello]

Would a piece of carbon work as a flat surface?

[Latticino]

Absolutely.  I used to blow glass into graphite molds and even cast molten glass into a couple as well.  Have to be careful regarding over chilling the glass to prevent cracking, but if it is not cracked and you get it up to around 1,200 deg. F for a moment before the annealing cycle you are good.  Note that the graphite I got back in the day was from a local shop that produced graphite molds for epoxy potting I believe (was a long time ago).  These were all cut-offs and scrap, so I got it for free.  The binder holding the sheets together would break down over time if allowed to get too hot.  I would preheat a little to avoid contact cracking, but typically kept down under 300 deg. F.  I used some of the sheet stock for the custom molds I made when I developed these blown tumblers:

[Gazz]

I used to make scientific glass and steel alloy structures years ago and the alloy we used was called kovar I believe as it had a very similar expansion/contraction rate as glass.

An interweb search will tell you more about it but I do not imagine it will be inexpensive.

[BillyBones]

Gazz, we use kovar in the shop where i work, some expensive stuff and a PITA to machine. The parts we make go into sensors for aircraft. Where in the plane i have no idea. But we use it becuase of its thermal expansion properties.