Independents

BjoernM21
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CORRECTION: Using the world "chemical" in the description of the bluing method Paul Gerber uses in the course is wrong.

The bluing of the screws is also the result of heat. The disolved "bluing salt" (an oxidizing mixture of potassium nitrite and sodium nitrate with traces of sodium chloride, potassium chloride and sodium bromide) can be heated to 300° C without the fluid evaporating or blackening the parts (like oil would do). Paul Gerber heats up the screws to 290° to 300° for the desired blue colour in this fluid to ensure the exact same colour of all four visible screws of different sizes (treated in one go). This colour control is exceedingly difficult by flame bluing, usually on a bed of brass shavings, because the way the screws are lying in these shavings has a direct influence on the heat transfer. The method used in the course gives the pupils a small time window to judge themselves visually what exact colour they want, and then stop the process by removing the screws from the fluid. It just shows again how keen Paul Gerber is to give his pupils the means to be actively involved in the creation of details of their watches.
Many thanks to you, skyeriding, for giving me a hint and an opportunity for corrections (I must have been asleep when Paul Gerber explained it all in the course, so I have now asked him for a private lesson...). And your kind comments are also much appreciated.
Björn

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