I thought I had some really promising results with the copper tests I did using the salt, white vinegar & ammonia recipe, so I decided to do a test matrix to see what would work best. (No, it did not include Trinity as played by Carrie-Anne Moss but next time you're in your home town, feel free to drop by and say hi to me & the family), I just tried every ingredient combination.
I got a whole bunch of interesting results. Long story short: Salt seemed to make it hard to disperse in walnut oil (it was all clumpy)
My best result is to only use white vinegar. I also thought I had an incredible blue with an ammonia/white vinegar combo, but after I mixed it with walnut oil, it reacted and turned green.
One other thing, as noted on some of the close-ups, I had reactions between the tests. My guess was that the vinegar & ammonia vapors reacted in the air just above the copper & oxidized it.
So, one more thing to try with copper before moving on: I need to do a few more tests with different types of vinegar. This time I’ll keep the samples a little further apart.