Blued screws are a tradition in clocks and watches but finding plain steel screws is a great difficulty these days as they are all stainless or zinc plated. I’ve had the idea of attempting to remove the zinc and blue screws in the past but as luck would have it, I have had the required screw in my fast dwindling stock. The current project requires an m4 x 80mm screws which is insanely long for such a small diameter and having no stock it was time to test the theory.
I purchased some cheap zinc plated screws off eBay and first placed the screws in dilute hydrochloric – 2M to be precise which removed the zinc within 30minutes. For those not able to source lab acids, I also used white vinegar on one bolt leaving it 24 hours but I got the same result so this should be doable for anyone but just taking a little longer to remove the zinc.
I then blued up the heads which is a skill I’ve been developing for a while. Heating it slowly through yellow, purple and when deep blue dunking it in oil. It is night time here and I used an iPhone but the screw is very blue and any imperfections are down to my lack of efforts in polishing the screw head before blueing due to this only being a test piece. I’m very pleased with the result which are not truly captured in the photo.