Tempering and bluing
Quite often in clock repairing special tools have to be made which then require hardening and tempering, and parts made or repaired that require bluing.
The problem is not usually in the hardening process, but in tempering to the correct colour.
One is often advised to heat the metal, watch the colours change, and quench in water or oil at a certain colour. Easier said than done!
The problem lies in the application of an even source of heat and in judging the speed of the oxidising colours.
With small items such as screws that require bluing there is no problem.
I have made a small bluing pan from a 3in disc of 1/16in brass with a 6in long steel handle riveted at a convenient angle. The plate is drilled with several holes to take screws of varying diameters.
The cleaned and polished screw is placed in a suitably sized hole and the plate is simply held over a small gas flame. As soon as the screw reaches the desired shade of blue, tipping it into a container of oil quenches the heat and maintains the colour.
Screws of differing sizes should be blued individually, as different diameters/sizes will require longer or shorter applications of heat to obtain the same degree of bluing. Whatever item is being blued or tempered, it must be clean and polished, and free from any form of grease, including grease from your hands.
When it comes to tempering larger items or bluing fancy clock hands of varying density and shape, the problem of providing an even application of heat, and thereby colour or tempering, is much harder.
In the case of bluing clock hands, bluing salts are commercially available and widely used, however I find the following method usually produces consistently acceptable results, and is also a lot cheaper and less hazardous.
I have made a steel container 7in by 3in by 1in deep, again with a riveted handle. The container should be made from steel about the same thickness as a saucepan in order not to buckle with the heat. It's a bit like a small tiying pan and has been made specifically long enough to take the minute hand for a longcase clock.
The container is half filled with dry fine sand, and the polished hand (remember not to use your hands!) is placed on top of the sand. The hand is then covered with more sand until it is completely covered and the container is nearly full. A steel washer is then cleaned up and placed on the top of the sand, the container is heated on a gas ring until the washer takes on the desired colour. The whole contents of the container are then tipped into a bucket of cold water. It should be found the hand has achieved the same even colour as the washer.
Personally I fmd this method works very well: the sand dissipates the heat evenly to the enclosed hand.
I think it's a safer, more predictable and controlled method.
The same process is used when tempering small tools and fly cutters to different temperatures.
The photograph shows the minute hand from a longcase clock, and washer used to check the heat when bluing. Both are evenly blued to the same colour.
As a footnote, when I was younger and first tried this method, I used one of my mother's best frying pans on the gas cooker ... she was not amused!
Ian Beilby, UK
