Fanning the Flames

Periodically on various forums I belong to, the topic of heat comes up. Metals and glass both use heat and/or fire for a variety of things and people often want to know the details of working with flame. So if you're considering torches, kilns and the like, here's some information for you.

General Information on the Use of Heat
You'll hear the term "annealing" used in both metalsmithing and glass work. It means two very different things in practice, while the actual meaning of the word remains the same. In either case, annealing means reducing stress in the material by applying specific temperatures to reduce brittleness.

In practice, annealing makes metal sheet or wire soft, while it makes glass durable. To harden metal, you "work harden" it, subjecting it to hammering, twisting, tumbling. If it becomes too hard, it becomes brittle and can break, so you want to anneal it.

Glass annealing is a little different. You know how when you put ice cubes into a glass of room temperature water, the first thing that happens is that the ice fractures? Well, that's because the ice didn't freeze at the same time throughout, so tiny "stress fractures" were created. Glass is a supercooled liquid. If it doesn't stay at the same temperature the whole time it is cooling (that is, if the outside of a bead cools faster than the inside), it will eventually fracture, just like the ice cubes. Small beads can be cooled in a fiber blanket or vermiculite, but if you're going to sell your beads, you will need to cool them in a kiln, which will only let them cool extremely slowly so that the whole bead stays approximately equal in temp during the cooling process.

Using a Torch with Metal
Metal requires a hand-held torch. The metal sits on a fireproof surface while the torch is aimed at it. Some metal soldering can be done with a butane torch, like you use in your kitchen, but that doesn't get hot enough to do larger pieces. Soldering/brazing/fusing torches can use propane and oxygen, acetlyline and oxygen, or natural gas and oxygen.

You have to consistently move the torch while soldering, which is why you need to use a hand-held torch rather than a mounted one.

Using a Torch with Glass
Glass is generally fused in a kiln, not at a torch. In a kiln, layers of glass are heated up until they fuse together. They have to be heated slowly so that the glass doesn't shatter, held at the appropriate fusing temperature, then cooled slowly (annealed) so that the stresses are removed.

Lampwork, which is done at a torch, is done with a torch that is stable, sitting on a surface, while the glass is held in your hands (unlike metal).

There are two types of lampwork glass. "Soft" is also known as soda-lime glass, made by Moretti (Effetre), Bullseye, and some other companies. Each manufacturer manufactures glass of a specific Coefficient of Expansion (COE). Glass can ONLY be used with other glass of the same COE. So you cannot mix, for example, Moretti 104 COE with Bullseye 90, no matter how good the colors would look together. (The COE is how much the glass will expand/contract as it is heated/cooled--so while glass of different COEs will melt together, it will crack and separate as it cools.)

Soft glass can be worked with a "hothead" torch, which is small and uses a single cannister of MAPP gas, but most people use an Oxygen-Propane system like the Minor torch.

Hard glass, also known as Pyrex, is what "Borosilicate" or "Boro" glass is. It's called Hard because of the heat needed to melt it (which is why Pyrex is used in cooking--you'd never put regular glass in your oven at 400 degrees). You need a bigger torch to melt Pyrex -- for example, a Major burner. That is also a propane-oxygen system, but the torch is designed differently, so the flame gets much hotter.

For either type of glass, in addition to a torch you need a kiln to anneal your beady treasures. For either type of glass, you also need good ventilation -- the fumes glass releases as you heat it are poisonous. For either type of glass you need protective eyewear because looking at the flare of glass as it melts will destroy your vision.

A few good books on heat and jewelrymaking:

Passing the Flame -- expensive, but worth every penny. Buy this one and you won't need another on beadmaking.

Introduction to Glass Fusing: 15 Complete Project Lessons & Ideas for Dozens of Additional Fused Pieces -- good guide to fusing glass

Jewelry: Fundamentals of Metalsmithing -- an excellent book on metalsmithing for the jewelry maker

Comments

[Cyndy]

But what about propane verses acetelyne for soldering silver? I want to set up a metals studio and am interested in the benefits/drawbacks of each. What about health/safety issues? Is one more efficient, quicker, better at detail work etc. the questions are endless.

[adept]

Hi Cyndy -

I will tell you what I know.

I use propane/oxygen for soldering for several reasons.

1) You can get propane tanks at any hardware store, so you don't have to worry about running out. Acetyline you have to get at a welder's supply.
2) I use propane/oxy anyway with my glass torch, so I only need one set of tanks.
3) Propane tanks are safe because they're made for any idiot to handle--your average Joe who needs one for his backyard grill has to be able to deal with the tank

People chose to use acetlyline primarily it burns hotter and cleaner than propane. Unlike propane, it's lighter than air, so it won't pool if you have a leak -- it will dissipate. Since you should NEVER keep your tanks inside your house, that doesn't worry me so much. Propane has a very distinct smell, so if it's leaking while I am working with it, I am going to know about it.

I've never had a problem with my torch not getting hot enough. I use a Smith "Little" torch with a high-heat tip. If you use the correct tip with the correct fuel, you shouldn't have any problem using propane for precision work. In fact, the studio I learned in used natural gas, which is not even as hot as propane!

I hope that helps some. I am able to tell you much more about the other gases because I don't use them. I have an acetyline tank because that's what I got with my torch. Everyone kept telling me that's what I needed, but eventually I figured out that I wanted to use what I was comfortable with, which was propane. For some reason, the acetyline scared me a bit.