Screw Bluing Fixture (unfinished)

Sorry guys. I forgot I originally posted this under members projects and not the clocks and horology forums.

Bluing steel screws and some other misc. parts in both watch and clock making is a common practice. These tools both serve to do the same task just with different size and shape parts, to temper the steel.

Essentially these are "holders" for the pieces being blued. The plate has multiple holes for different sizes of screws, whereas the tray when filled with brass shavings surround an oddly shaped part to help heat it evenly. The tool is held over an oil lamp (or a propane torch in my case) until the steel tempers and starts to oxidize. For a quick idea of the process and how it works keep reading....




Once a screw for example has been turned, oil hardened and polished, it needs to be tempered. Heating the steel evenly oxidizes the surface at the same time it tempers the steel. Tempering it takes away the "brittleness" that hardening gave it, but allows it to retain its strength.

It's the oxidation of the surface that causes the steel to look blue as the thin layer of oxidation causes the light to refract. As the steel is heated, it will go through multiple colors, straw, brown, purple, dark blue, light blue, then finally a gray silver. If you've ever welded, you can see this coloration in the steel around where you welded based off the temperature it reached.


Tempering screws this way in horology is done for 3 main reasons

1. Once the screw has reached the blue color the steel has been appropriately tempered relieving the internal stress and reducing brittleness without compromising the strength of the steel. The color acts as a temperature gauge during the process

2. The oxidation of the surface acts to protect the part from scratches and blemishes as well as surface rust or degradation over time

3. For aesthetic reasons. The blued steel stands out against the brass plates and wheels of the clock. This was originally only done with high end or handmade watches and clocks, but not to those from factories so it served as a sign of craftsmanship as well.

Blued steel screws can be found in many other places as well. On antique/vintage firearms, knives, etc.
Modern firearms typically use a cold bluing process or a type of finish applied to get the blue color. It creates the same surface oxidation but is not a replacement for tempering the steel. Thats not much of an issue though as "most" gun parts are also not handmade, and the ones who do handmade their parts should be familiar with the difference.
 
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