Polishing
After some friendly goading from my closest dagurreian friends, I went out to the castle tonight to get some more hands-on practice with polishing. I’m sticking to bare copper plates still, since I don’t feel ready to tackle silver yet. True to my friend’s advice, I began to learn a few things that I didn’t read about in books – and confirmed a few that I had.
Fact 1 – Flat metal plates are not actually flat.
This is one I hadn’t found in the books. I started out by taping a 24 ga. copper sixth plate to a piece of 1/4″ acrylic and rubbing it by hand on a piece of 1 micron 3M polishing paper that was sitting loose on my workbench. After a few minutes I had a very nice mirror finish on the copper. In the two or three dime size and smaller places where the paper actually touched the copper. Hmmmm. It looked flat… At first I thought it was the workbench being too rough, so I put the polishing paper on a piece of 1/4″ ABS plastic. This improved things but not much. I decided to try a coarser polishing paper. That’s when I discovered the next fact.
Fact 2 – 9 micron polishing paper does not produce a mirror finish.
I suppose this is a no-brainer to others, but I have to admit I was a bit surprised about how big the scratches looked. I can see that this grade is for initial removal of pretty big surface problems. Not for polishing. The bigger abrasive did manage to hit more of the plate however. I guess those valleys aren’t all that deep.
Fact 3 – You can’t stick a copper plate to a velcro sanding pad with velcro coins.
I thought that would work but it didn’t – I’m not sure why. I will have to come up with a different method if I want the plate on the sander.
Fact 4 - Three micron alumina powder doesn’t produce a mirror finish either, but it looks a lot better than 9 micron paper.
For the last experiment I taped my plate to the ABS plastic using double sided sticky tape, put 1/4 tsp of alumina powder on it and spritzed it with distilled water. I then polished it for 10 minutes on speed one of my ROS using a plain foam polishing pad. This did produce a pretty good finish, but I still wouldn’t call it “mirror”. There were also quite a number of distinct but rather random scratches that I expect are the real devil in getting the process under control as you improve. I don’t know if they were from contaminants, the bare foam pad or what.
It did give me a sense of at least one promising method however. Lots of details still to work out though. Mounting methods (sticky tape sticks too well), succession of powders, cleaning methods between powders, figuring out those little swirly scratches, etc.
I also proved out some other things I had read or heard – clipping or grinding the sharp corners is a good thing. They don’t catch the polishing paper or foam so much that way. Also burnishing the sharp edges of the plate is a pretty good idea too. Ditto on the reason. It would probably be easier with a real burnisher though than the piece of flat brass I actually used. :)
I think I will go make a decision about rouge and charcoal and maybe some of that “green” powder that Irv Pobboravsky was talking about on the CDags site. I need to try silver soon. I also ordered some cotton batting for my iodine fuming box. I need to get that ready too.
Daguerreotype Process | andy | February 23, 2009
acrylic, alumina, castle, copper, daguerreotype, daguerreotype process, iodine, micron, Plate preparation, Plates, polishing
Glad to see you’re making progress!
Plates certainly aren’t flat and I think the thinner you go the worse it is. The 16 ga. plates I use are pretty flat but not perfect. I was thinking that the extra padding used on buffing paddles, under the flannel or suede, might help address the problem.
Yes, the “give” of the foam polishing pad made it much better at putting abrasive in contact with the whole surface of the copper. I’m still wondering about those random swirl marks though. The pad was new out of the box. Maybe it had debris from the factory on it. Next time I will vacuum it or wash it or both.
Have you ever made a plate that had no visible marks on it at all?
I have yet to make a plate with no visible marks. Though a lot depends on the angle of light I view the plate. Since I’m using a wheel (soon to be orbital!), if I hold the plate so the light is the same direction as the final polish marks, it looks nearly perfect. Holding it the other way makes it look horrid. Also, the pressure has a lot to do with it. When I start with rouge I press pretty hard and slowly reduce pressure over about 10 – 15 rotations. The last of which barely touch the wheel if at all. That seemed to help a lot.