Hi all
This seems to be a multiple subject thread so I hope you dont mind me adding what I feel is a little clarity to things.
Firstly Jack Rowes method of tempering a spring (actually drawing the temper we say here) that is after heating to cherry red and quenching the next thing you do is draw the temper by re heating again. If you listen to him he is using the old flare method using Whale oil a very common method here for making small springs up to the 1950s but now not possible and rightly so. Is there an alternative yes! Lard works well it burns at about the same temperature as Sperm whale Oil. Next is what is cherry red? Now as simple as it may sound it is hard to get right especially if you are heating up the metal under any form of electric light because it changes the colour considerably. I was once lucky enough to visit the Black Smith and Farrier School here in Salisbury and the forge rooms had extremely low level of lighting to the point of darkness so the tempering colours could be seen more clearly. When flame treating steel subdued lighting is a must. Now for a very old tip I use for tempering springs using an open flame after you have heated the steel to cherry red. If you use an open flame to draw the temper to the correct colour the thin parts of the steel heat up faster than other parts and you end up with more colours on the steel than Josephs Coat and the spring will more than likely break. The method I use is to heat the part in Silver Sand in a metal tray in doing it this way the sand absorbs the heat very slowly and evenly, so you burry your part just below the surface it will heat up slow even and you can move some of the sand covering the part now and again to see how things are progressing, when the correct colour is attained quench it in water or oil doing it this way its temper will be even,
Nitre Bluing the components for this is many and varied. Now during WW2 in many countries but not the USA as far as I know, UK, Germany, USSR, used NPK Fertilizer because pure Potassium or Sodium Nitrate was hard to get but lots of fertilizer stocks at the start of the War, and these mixtures gave differing blue colours. I would like to say here that heat liquidised Potassium Nitrate is an extremely powerful oxidiser if it spills on any combustible material that includes YOU!! It bursts into flames instantly, and you for the Hospital Burns Unit.
