If you heat steel up the right temperature, you can get some cool colors. I've been on a bit of a bluing kick, that is, heating up screws and wheels and getting them to turn a magnificent color-for no other reason than it looks INCREDIBLE.
There are a few different methods to turning your steel blue, each with their own sets of pros and cons. Being an amateur at this, I've been giving them all a try to see which I prefer and so that I can further understand the process.
Here's the kiln at my disposal, initially I perceived this as the best method as you can precisely control the temperature (ha!) and therefore control which shade you want. It does have the added benefit of doing large batches simultaneously.
I used the kiln for the ETA 6497 pictured above. Looking closely you can see variation in the colors on the screws and wheels. On the crown wheel you can see a yellow area, this is where a piece of dust landed caused non uniform heat dispersion. One of the reasons there's variation in the colors is that there are currents in the heat flow within the kiln, even over small surfaces.
I tried to remedy this by building little houses out of brass to insulate the parts, but even that wasn't super effective. Time to try some other techniques.
You can get a container and fill it with brass shavings (pretty common) and slowly heat it with your piece inside. The reason I don't really like this method is because you can't directly see your work piece and lifting up the lid and poking around in the brass will disrupt the heat-and that's no good. Right now, for screws, I'm into waving them over an alcohol lamp while in a brass jig.
And by jig I mean a piece of brass with a small hole in it. I experimented with different thickness of brass and hole placement. If the brass is too thin or the screw holding hole is too close to the edge you'll get non-uniform bluing as heat distribution wont be even. This jig has served me pretty well so far.
You can see how the screw starts out, it's pretty important to polish the screw head before bluing. Having a polished and uniform surfaces will help the oxidation layer (color) take hold at an even rate. Many screws that I pull out of movements are also plated, so polishing that plated surface away is necessary.
Steel will go through a different colors before getting to blue (which is the final color and easy to go past). It begins at a pale yellow and darkens to brownish then turns purple/violet before quickly and finally becoming blue.
Once you get to purple it's a good time to slow it down and move back from the flame a little. The blue creeps in from the edge then it goes pretty quickly, plus you want the color to be uniform. It's easy to get splotches or different colored edges. It's best to not mess up, the more times you try to get something to blue the more you weaken the metal, and with screws which are meant to be cranked down tight, you don't want to do this process too much to a single screw.
Once you get it to the color you want, quench that sucker. The heat within the screw and held in the jig will cause the color to keep changing.
Many people suggest doing screws in batches so that they're affected by the same amount of heat and come out the same color. This hasn't been my experience at all in my short amount of time bluing screws. Perhaps with a higher end kiln this would ring true, but above you can see the results. The ETA on the left had all the screws done in a single batch in the kiln and the wheels were done in a separate batch. I built smaller houses within the kiln to minimize any draft or current and still the variation is very noticeable.
On the right, the Seiko NH35 has all screws that I blued individually over an alcohol lamp. Each screw is very uniform, at least in comparison to the kiln screws. There's a little variation in the shade of blue, but again, eyeballing the color on each one is still more accurate than trusting the kiln to distribute heat evenly.
Next step is to make some display casebacks to show it all off.