Magnesium castings require protection from atmospheric attack; the factory soaked the castings in a Dichromate bath. The castings were then painted silver for hubs and brake-plates and matt black for engine parts.
The constituents required for a one-gallon bath are:
|Quantity||Item Description||Stock code|
|500 gramme||Sodium dichromate||301304M|
|250 gramme||Magnesium sulphate||291172L|
|250 gramme||Manganese (2) sulphate||291474W|
The stock codes are for owners in the UK where the chemicals can be obtained from Analytical Supplies - Tel No: 01332-831671.
Apparently the parts are submerged in the solution for 24/48 hours.
I have ben advised that there is a potential danger in re-dichromating old magnesium parts. It is that the process can cause hydrogen enbrittlement, which could be very dangerous in the case of hubs. Perhaps it's safer to just paint hubs with a heat resistant paint.