Big Bell:

Friend Paul spent a previous life as a firefighter, had access to some out of date CO₂ cylinders, and wanted one made into a bell. Here is the result. One of the others became the bell jar for our vacuum system..

When he brought the cylinders over, they were in mucho rough shape. So, the first order of business was to take out the valves and chuck them in the big lathe to scrape off the paint, rust, and crud and get down to clean metal. The lathe was also used to cut off the bottoms, with the Bosch jigsaw used at the end to finish the cut.
The bell potential was evident as the final turning operation was done; the thing started ringing and making the tool chatter. I'd estimate it hit 150 dB or louder before I could stop it! Literally slammed our eardrums into their stops with a great deal of pain.

Paul wanted the arrangment at the top, so we made that next. Forge work is fun in the wintertime. That big 5/8" stock bent like a limp noodle at yellow hot. Then it was welded into the plate from the back side, and the plate welded onto the cylinder. At this point we had a ringing bell, but it obviously needed some surface coating. This caused us some pause, as this thing is meant to be hit, so paint was probably out as a practical coating. It would probably also affect the tone.

After some thought, we decided to blue the thing, using the old rust bluing method Doug has recipes for. Experience with several formulas combined with some advice by older gunsmiths lead us to use the Zischang formula. Roughly, this is diluted aqua regia with some iron dissolved in it. For the first rusting, though, we used a stronger formula that is ammonium chloride based, so as to ensure an even "take". The process goes like this:
1. Get workpiece completely free of all surface contamination. Really clean. If distilled water beads rather than sheeting when sprayed on, it's not clean enough.
2. Apply the formula to the surface evenly. If it doesn't go on even, see above.
3. Put it in a humid place to rust for a few hours or more. See our enviornmental chamber.
4. Place workpiece into already boiling water for 10 minutes or so. The water must be free of dissolved gases.
5. Using 0000 steel wool, take off as much of the coating as will come off. This will make an evil mess of fine black powder, so be ready for that.
6. Go to #2 above, and repeat 6-15 more times.
7. Seal surface with something. We used linseed oil. This oxidizes in air to harden, and preferentially gets the oxygen before it can get to the steel and rust it so is a good choice for steel. Linseed oil takes a long time to harden fully, so we hung this over the woodstove for a couple of weeks before waxing it with floor wax. The rusty I–beam you can see behind the bell is leaning on the same stove.

The result is phenomenal. A light tap rings this loudly and clearly, and it rings and rings and rings. This could definitely annoy the neighbors, or be heard for miles. Paul is going to make a leather covered wood striker for this, and a stand. With the soft striker it ought to be a little tamer, which would be a good thing. The finish seems just right for this. It will take strikes from a walnut knocker with no visible damage. It's hard to take a good picture of a shiny black thing, but in person the effect is very nice. To accelerate the rusting, we use a chamber Doug built that is just a 2' x 2' x 4' masonite box with a door on it, which has a hotplate inside. On the hotplate is put a gallon sized container of water, which is kept just below simmering heat. Various hangers in the box allow for workpieces to be supported without contact on their bottoms. The outside of the box is insulated with R–Max. We run the temperature in the box at about 100° to 110° F, adjusted by the hotplate setting. What you are trying for is a coating of very fine grained rust. When things are working right, it sparkles a little. The arcane secret formulas were developed to get this to happen fast, without the rust also becoming coarse pits. Basically, less is more here. You could try diluting regular ammonium chloride / zinc chloride liquid plumbing flux about 10::1 for starters. 2% ammonium chloride by itself works great. You don't want condensation on the workpiece, which washes off the formula and generally makes things look bad and uneven. On the first pass, both the work and the chamber are cold, so no problem, they will heat together when the hotplate is turned on. On subsequent passes, if you work fairly quickly, the work will still be hot from boiling it, so again, no problem. But if you put room temperature work into the steam bath, it will fail.
The boiling step changes the brown Fe₂O₂ rust into black Fe₃O₄ magnetite. This is a little less oxidized than the brown stuff, and will eventually re–oxidize back to brown if allowed to. This is why it is important to have the water already boiling, so it will have zero dissolved oxygen in it while the transformation takes place.

Sources:

Information on rust bluing:
Gunsmithing, by Roy Dunlap, 8117–0770–9
Firearm Blueing and Browning by R.H. Angier, ISBN 0–8117–0610–9
Both books are published by Stackpole Books, Harrisburg Pennsylvania, and can usually be found at gun shows. In fact, that's about the only place you would find them. Worth what they cost. You will have fun trying to find the chemicals by the old–time names! A lot of the old formulas are pretty toxic. That doesn't scare me, but since we are getting such fine results with non–toxic chemicals, why bother with the dangerous stuff?

Boiled linseed oil and Johnson's paste wax were obtained at Lowes.

Some sources for cylinders are:
The local firehouse. When they get really nasty, they just toss them out. These needed nearly .1" taken off them to get below all the rust.
The local guys who provide gas for welding. Same deal here. You can always just buy one at this source and let the gas out...while Doug weeps.

I got the gallon size container at WalMart. Kind of a big flower pot shaped thing, large at the top, so it's good for this. Claimed to be stainless, made in India. It did look like stainless steel, but rusted the first day doing nothing other than boiling pure water.

We use a turkey cooker we got at Lowes for boiling big things. Boy, does it ever heat up quickly, and the room along with it. Another winter pursuit.