Purple Steel Finish

Recent discussions in the Blank Firing category about Purple colouring on some steel guns reminded me of a review Francky wrote awhile ago on MGC's MP40.

Very similar purple colouring can be seen on the modelgun too

Refer to
https://mp40modelguns.forumotion.net/modelgun-reviews-f4/mgc-mp40-t240.htm

for more photos of this example.

And Jim's Modelgun MGC MP40


Compared to these Blank Firers converted from real weapons:-


Refer https://mp40modelguns.forumotion.net/blank-firers-f14/blank-firing-tt-tokarev-1937-t1750.htm for more




Can anyone recall the discussion about chemically processing steels which resulted in this purple hue

Copied from smootik's post 15/10/09
see https://mp40modelguns.forumotion.net/blank-firers-f14/blank-firing-tt-tokarev-1937-t1750.htm for further discussion

pitfighter wrote:

Who knows the nasty stuff they used to use to color metal

Friend who worked on steel production said it is most likely from heating treatement. When steel is heated and then suddenly cooled in oil (to change its properties), steel surface colour also changes depending on maximum temperature reached.

He is not sure if there is a particular treatment that would change colour long time after manufacture (like slow oxidation).

Table below is scanned from an old Polish book on steel processing.
Colours are approximate only, same goes for naming (we need a woman to give names to colours ;-) )

Quote :

250C = yellowish / purple
260C = purple
270C = dark purple / red
280C = dark blue / violet
290C = dark blue

It is interesting to note that in the past steel has been used sometimes as an approximate max temperature meter. In range between 200-400C it changed surface colour (after cooling of course). In range 500C-1300C it glowed with different colours.

He warned not to attempt heating steel objects at home, unless it is known they are pure steel. In the past, smaller steel parts (like nuts, bolts) have been sometimes plated with cadmium (poisoning kidneys!), not zinc.