Straw Finish, What is it?

[xzw151]

I hear the term "straw finish" applied to Lugers in particular, such as "95% bluing. 97% straw finish" etc. So what is straw finish? I tried a search, but my google fu must be weak today.

[Asphodel]

A 'straw finish' or 'strawed' is the first step in a 'heat blued' finish. As heat is applied to polished steel, it develops 'oxide colours' beginning with 'light straw, just barely visible, continuing through purple-flecked straw, purple, and on through various shades of blue.

You can read explanations of the colours, and their relationship to the temperature of the steel, by doing a 'google search on 'tempering colours'.....er....'tempering colors'....many people here can't spell English correctly.

'Heat bluing' or 'strawing', traditionally, involved holding the steel part over a small alcohol lamp, watching for the colour as the part warmed, then quenching quickly in 'neutralised olive oil'. 'Neutralised' olive oil is made by putting best quality olive oil in a glass jar, adding a quantity of thin lead shavings to the oil, allowing the jar to sit in sunlight for a couple of weeks time, then decanting off the upper part of the oil. This reacts and removes any free acids from the olive oil.

You can readily polish and 'straw finish' or 'heat blue' parts at home.....its an easy job.

Probably, a Parabellum pistol part would have been strawed in some production process, say with a conveyor and heat source, timed so that the part was dumped into a vat of oil at the exact moment of the desired colour.

Traditionally, sperm whale oil (spermaceti or 'parmacetty') oil, would have been preferred to olive oil, but that oil is an expensive 'black market' material today.

cheers

Carla

[tankerman]

Thanks for that excellent information Carla.

[rolo]

I think I just *swooned*. That is an accurate and awesome write up Carla.

Drawing color is still used today by lots of artisan craftspeople. It's the oldest way other than destructive testing (which kinda defeats the purpose if you are making a one-of) to determine proper temper of a piece of steel that has been quenched after heating to non-magnetic or critical temperature.

There's nothing I enjoy more than watching colors run on a spring I've just polished up after forging. ATF makes an excellent substitute for whale oil, for good reason. The first automatics used whale oil for lubrication.

[QuarterBoreGunner]

Carla, that was a brilliant explanation, thank you