Straw parts

[Kyrie]

Originally Posted by k98mike

I think Lugers with straw small parts are more attractive, why was it done? The straw finish is supposedly less effective than standard bluing; Did they not know? Was it just considered more attractive?

There is a basic misunderstanding here. Straw (and fire blue) colors are not a finish, are not applied as a coating, and are not primarily intended to produce corrosion resistance.

The yellow and blue colors on small parts are by-products of the heat treatment of those small parts to attain a specific hardness to reduce abrasive wear without inducing brittleness.

Here is a link to a document that details that heat treatment process (historically called fire, or flame, heat treatment), and the temperatures at which specific colors appear (each color denoting a specific range of hardness):

http://navybmr.com/study%20material/...14250A_ch2.pdf

This heat treatment produced hardness has, as secondary and incidental effects, the production of attractive surface color and a very limited increase in resistance to surface corrosion. But this color and small increase in resistance to surface oxidation is just a by-product of the heat treatment done to reduce part wear due to abrasion.

[Norme]

To appreciate the range of colors produced by heat treatment one need look no further than the hold-opens on Imperial era Lugers, some of which display a spectrum of colors (see photo).
Krieghoff Lugers are frequently encountered with a mixture of yellow, orange and vivid blue small parts, likely a result of erratic temperature control.
Norm

[DonVoigt]

Originally Posted by Norme

To appreciate the range of colors produced by heat treatment one need look no further than the hold-opens on Imperial era Lugers, some of which display a spectrum of colors (see photo).
Krieghoff Lugers are frequently encountered with a mixture of yellow, orange and vivid blue small parts, likely a result of erratic temperature control.
Norm

Norm,
that is a great picture, it shows on the one piece the range of temperatures reached on the hold open, from the bright polish to light yellow, straw, brown, red, purple, bright blue, peacock blue, and then into grey.

Many have seen the attachment below often posted before showing the colors and corresponding temperatures.

Kyrie,
Thanks for your post, I do hope it puts a stake through the heart of the misconception about "staw" and corrosion.

[Kyrie]

Originally Posted by Norme

To appreciate the range of colors produced by heat treatment one need look no further than the hold-opens on Imperial era Lugers, some of which display a spectrum of colors (see photo).
Krieghoff Lugers are frequently encountered with a mixture of yellow, orange and vivid blue small parts, likely a result of erratic temperature control.
Norm

Or could be a good example of selective heat treatment. Plant the rear of the part in a heat sink, flame harden and draw the front of the part, and the boundary between the protected/unprotected sections of the part can show as that heat gradient.