For the next attempt at the patina, I had to think of a more fool-proof way to mask the areas of the assembly that are not allowed to come in contact with the chemical solution. I have used plastic packaging tape in the past, so I tried it this time. But the one I bought this time is extremely difficult to take off because the glue is too strong. That makes it also difficult to apply tightly around the blade since once it gets stuck, it cannot be corrected. And, the masking around the filework was a major headache-inducer, there the tape was totally insufficient.
So I needed something that is resistant to water and water-soluble chemicals both acidic and basic, hot and cold, something that will show me clearly what is masked and what is not, something that can be applied with high precision and good adhesion to complex surfaces and simultaneously can be removed easily later on without damaging the patina.
And after some thinking, I did come with a solution that worked really well. I made everything pink!
© Charly, all rights reserved. Click for full size.
That is the cheapest nail varnish that I have seen at the local drugstore (2,-€ per bottle). Afterward, I have added the packing tape on big surfaces, but I think it was unnecessary and just me being overcautious.
© Charly, all rights reserved. Click for full size.
I proceeded to make the patina on brass fittings by alternating between acid bath (HCl, very diluted) and polysulfate bath (with occasional brushing with a soft brush under running water) until I have received a color that I was content with, which is sort of metallic blue/brown/dark gray, very similar shade to the oak-tannin patina on steel.
Cleaning off the varnish was a bit of a hassle and used up a lot of paper towels and acetone, but the important bit is that it could be done, could be done well (it was easy to spot uncleaned places) and did not scratch the patina on either the fittings or the blade. I will probably buy heaps of cheap nail varnish, it opens up great possibilities.
For a masking agent, you might want to try one of the ones made for plastic models — especially the clear canopies (the framing on a model airplane canopy can be one of the hardest things on earth to mask . . .) . Mr. Hobby makes a couple of different liquid masks which are designed to be used with paint and an airbrush. There are also quite a few friskets out there — a clear film with an adhesive on one side. These are designed to keep paint out, but not pull up the paint already in place.
For the dying of a knife, you might want to check out the liquid masks. They go on easily and pull off like rubber cement.
Come to think of it, I think that they are just thinned rubber cement. Hmmm.
Thank you for the tips, Oggie. If I find a shop with modeling supplies or art supplies somewhere nearby, or if I happen to be around one during one of my infrequent travels, I am going to ask around about these. Alas, I am unaware yet of any such shop in my vicinity, and ordering these things that cost just a few bucks a bottle is not worth online purchase, the shipping would be more than the purchase.
Try using cotton wool rather than kitchen towels for nail varnish removal, that way you can use more of the acetone by tearing off the first layer of cotton wool, then the second, then the third etc depending on how much acetone you started with on the cotton wool, also you lose far less to evaporation than you do with kitchen towels. Cotton wool is stronger too so you can wipe more firmly but there is still no risk of scratching. On the rare occasions I buy it -- because it lasts me ages -- I get rolls of cotton wool, by far the cheapest way to buy it plus you can tear off exactly the correct amount for the job at hand.
That’s really clever. I think you got a great color, very attractive and it should work well with your other colors.
I would second Jazzlet’s suggestion but I use Q-tips myself due to working on very small things. There is a Dollar Store relatively nearby and I can get them there very cheaply by the hundred. I have no idea if this would work but sometimes I do things the other way around: I mask what I want to work on (in this case, your brass fittings) and then I spray paint the item with some sort of cheap thing. For example, cheap hair spray. You would have to test it to see if it will withstand your patina process, but for this very reason I have a can of “Aqua Net Hair Spray” in my house. I would not dream of putting it on my hair. I also have several cans of various clear varnishes, lacquers and so on. They do come off fairly easily with Q-tips and acetone.
Charly:
There are a couple of online hobby shoppes. Try Squadron.com.
@Oggie, shipping from an American shop like Squadron.com to my location costs about 70 bucks, so that is definitively not an option, for that kind of money I can buy enough nail polish for an elephant. I do not shop on Amazon on principle (shitty company, treats employees like trash), and on other online shops that reside in Czech those things you recommend are quite cheap, but still, the shipping is nominally 4-10 bucks per package, so I would need to know exactly what to order and what quantity, to order just one bottle for experiment is not financially feasible. I will look if these things are sold at the retailer where I buy brass profiles.