Bronze problems, stuck mechanism

Romain · Post by **Romain** » Tue Apr 19, 2005 9:10 am

2 weeks ago, I bought another antique crossbow mechanism. I is quite nice but completely stuck.

I tried to make it functional again by first plunging it into Coca-Cola, then by soaking it in WD40, but to no avail. It is as stuck as the day I bought it.

Romain · Post by **Romain** » Tue Apr 19, 2005 9:12 am

Would you know a trick to set the moving parts loose again ?

Stephen Selby · Post by **Stephen Selby** » Wed Apr 20, 2005 4:37 am

For un-sticking the crossbow mechanism, I suggest a two-week immersion in a solution of 2 parts of black treacle (molasses) in 8 parts of water. followed by four weeks in light benzene. The latter may be cargenogenic and the fumes should not be inhaled.

For the arrowhead, it requires a coating with a substance marketed under the name of 'Incralac.' See:

http://www.australwright.com.au/DataShe ... Lacque.pdf

Romain · Post by **Romain** » Wed Apr 20, 2005 12:47 pm

Bede wrote:I have a museum curation article at home on how to permanently fix bronze disease. A friend in Japan had problems with some arrow heads and he followed the instructions. He said it fixed the problem.

Are you interested in the steps involved?

Yes, Bede, I'm interested.

I do not care for the resale value, I do not plan to sell any of these arrowheads, I even think the disease patches are quite beautiful, however, I consider it my duty to stop the damage speading on a 2000+ years old artifact.

Stephen, I never heard the words "black treacle (molasses)". Is it something you can buy anywhere ? Benzene is definitely and highly cancerigen. I do not even think you can buy any in Europe anymore.

Stephen Selby · Post by **Stephen Selby** » Wed Apr 20, 2005 1:08 pm

Treacle is a thick, sticky black sugar (糖浆). It acts as a reducing agent on the copper salts. In Hong Kong we can buy it in the grocer's shop.

Dave · Post by **Dave** » Wed Apr 20, 2005 1:42 pm

Molasses can be obtained from horse saddlery shops, or farm animal food warehouses if that's any help.

Dave

Dale Proctor · Post by **Dale Proctor** » Mon Apr 25, 2005 3:58 am

Hi Romain,

Regarding freeing up your trigger mechanism: I would find a soft wood stick such as pine and use it as a mallet. The soft wood will dent instead of your bronze. You should be able to apply some force to it that way. The trigger looks to be in real good condition so it shouldn't hurt it any. There may still be dirt and crud inside the box blocking the mechanism and banging on it should knock that out. If that doesn't do it I'd consider gently heating the box with a propane torch. Don't heat the pins. It will cause the box to expand and then you may be able to knock the pins out.

If you haven't done this already, I would try it before dunking the box in molasses or something more complicated and lengthy.

Stephen Selby · Post by **Stephen Selby** » Mon Apr 25, 2005 4:27 am

Dale's method is real 'brute force'. I am not very keen on it. However, if you can reduce the quantity of copper salts with a reducing agent, I would see no problem in heating the whole assembly in hot water in the hope that the components around the axle pins would expand quicker than the pins themselves, which are solid, and then tapping lightly with a mallet.

Heating with a blowtorch will certainly cause this ancient bronze to crack, as well as encouraging more oxidation of the bronze surface where in fact you want less.

Romain · Post by **Romain** » Mon Apr 25, 2005 9:19 am

I must confess I tried to hit the pins already, with a slip of wood between the pin and the hammer.

I tried to tap not too hard, but I already got a tiny damage because the pins are pierced perpendicularly close to the tip where another smaller pin would secure them in place.

I immediately stopped hitting.

Not having mollasse at my disposal, I decided that coca-cola would be a similar kind of sugar dilution and I sacrificed 2 cans in order to sink my mechanism in it.

It sank on friday and today seems as stuck as before. I'll tell you what happens in the following weeks.

I cleaned the dirt remains that were inside with water. I also tried hot then cold water but nothing bulged. It was not boiling water as I was afraid to crack the mechanism.

I do not see myself using a propane torch... maybe I could use my heat gun which should be less brutal...

Stephen Selby · Post by **Stephen Selby** » Tue Apr 26, 2005 1:09 am

Coca Cola is a good idea. In fact, freeing up locked crossbow mechansims is probably all that it's good for.

Change the coke solution once a week.

S,

Dale Proctor · Post by **Dale Proctor** » Wed Apr 27, 2005 6:54 am

I suspect I mis-interpreted functional to mean that you wanted to use it in a replica crossbow. If that isn't the case, what I suggested is rather harsh, as stephen pointed out. It sounds as though it is too fragile for that from your results with the hammer.

If you just want to free the mechanism, molasses, if you can get it would be your best bet. The darker the better. It isn't the sugar, it's the stuff that gives molasses its color that does the trick. It is a chelating agent and will clean rust and patinas off metal without harming the metal. Cut it with water so it's liquid and not syrup.

Coke has phosphoric acid in it and will eat away at the patina and the metal. It just eats metal far slower than the patina.