Is my Fork Yoke (Trippletree) Magnesium

Hello
I have purchased a Norton which has come with a set of original Ceriani GP forks
I want to upgrade these to a disk setup so want to sell these forks
Invetigating these seems to suggest that the top and bottom yokes (trippletrees) can either be alluminium alloy or magnesium alloy
They are very light and appear to have been sand casted

So.... question ..... how can I tell if these are magnesium ?

The only way I know is if you set light to them and you cannot put them out then they are magnesium
Is there a better way to determine what they are made of

Thanks ..... Richard

You can touch it with a file, cast magnesium tends to be alittle darker in color than aluminum, more grey.

I've seen die cast and sand cast Ceriani clamps but they have all been aluminum.

If you put a small drop of caustic soda solution on them, it they fizz, they are aliminium. If the fizz and turn black they are copper bearing aluminium. If they fizz and turn white they are magnesium bearing marine grade aluminium. If they don't fizz they are probably over 90% magnesium. Don't forget to wash off the caustic soda solution when you finish the test

thanks, I will try the test ..... very carefully

Magnesium will dissolve, quite readily, in seawater.
So may be quite violent in caustic.

You are right to be cautious. !
If it reacts quite vigourously, its likely to be MAGNESIUM though.

As mentioned above, magnesium alloys generally have a grey look to them.
Where aluminium are quite silvery.
Unless they are painted, anodised or chromated, this is a pretty fair quick-n-dirty test.

Part of the old process of applying chromate passivation to magnesium was a pickle in dilute caustic soda solution. The chemistry is different to that of aluminium. With the test I mentioned, there were two solutions used, one drop of dilute caustic solution, wait a few seconds, then if the spot turns black apply a spot of dilute nitric acid, if the black spot disappears the alloy is copper bearing aluminium, and if it remains, I think it means both copper and silicon are present.

Go to a library :

http://www.astm.org/DIGITAL_LIBRARY/STP ... reword.pdf

Library ??
The web IS the library - you are a bit behind the times ?!

Caustic will CLEAN magnesium for pickling.

There is nothing strongly acid or alkali in the dichromating bath for magnesium,
as these would damage the surface you were trying to passivate..