This Corrosion

Well this patina anyway. A couple of the original screws holding the head into the pot were missing, one'd been replaced with a different shape and size screw the other was just left missing, the remaining six were all damaged and rusty. I decided to replaced eight.

 The originals were small imperial slotted self tapping screws, although I identified the thread I forget what they were -I certainly couldn't find any identical replacements online. Eventually I found a company called Model Fixings who seem to specialise in model helicopter bits who had a huge range of tiny screws. I ordered a pack of No2 Slot Countersunk Self Tapping 9.5mm screws in Stainless Steel.

A couple of days later a bag of 100 shiny bright wood screws came through my letterbox. They looked to be about the right size. Just one problem though: the old screws being, probably predating stainless steel, were blackened by time rather than bright silver.

To keep the instrument looking authentic I'd have to patinate the new screws -or their heads anyway, the threads will be hidden in the wood so won't matter. Stainless Steel, unsurprisingly, is difficult stuff to mark. There's probably patinating, darkening and etching solutions that'd work but I didn't have any of those. What I did have was some drain cleaner and a gas hob. I was pretty sure I could do something with those.

 First up I mixed a strong lye solution in a jar. If you're making lye (Caustic Soda in Water) always add the Caustic Soda to the water and bear in mind it's going to get pretty hot. It also gives off Hydrogen gas. Dangerous stuff and to cover my back in case some avid internet reader burns their house down I suggest nobody actually does this.

Using pliers to hold a screw head into the gas flame I heated the head to red hot

Then dipped it into the lye. Actually bearing in mind this solution is chucking out Hydrogen gas which has an autoignition point of about 536 degrees Celcius and red hot metal is probably at least 500 degrees Celcius I let it cool from red before dunking it into the lye -I think the metal pliers worked as a heatsink anyway so it only took a second or two.

I then returned the screw head to the flame, dunked it back into the solution agains and repeated the process a few more times then let it cool. When I'd done the same thing to 8 screws I dropped them in a sink of water and cleaned off the baked on Caustic Soda with a scrubbing brush. I figured with enough water it'd be too diluted to burn my fingers too badly -gloves might've been a good idea but it went okay.

The picture below shows the 8 newly patinated stainless steel screws. The shiny one is a spare stainless steel screw looking how the others had originally and the three on the right are some of the old aged screws.