copper & paint

[enginedriver]

does anybody know anything about copper?

i read somewhere (maybe in the White Dwarf) that putting pennies in your bottles of paint will keep them from drying out - something in the copper, i think, plus they help mix the paint when you shake the bottle. well, it works. i tried it out and the pennies have kept my paints (i use GW) from drying out.

i'm thinking about finding a copper plate to use as a palette, but i'm interested in what's going on here. does anybody know?

[watwe]

no this is a new one to me id be interested to hear why/ if this works .

[thewartoad]

Never heard of it? If you find anything out let us know. Cheers!

[Henrix]

I have bad experience with using copper coins in my paint. They corroded over time and made the paint useless. Now I won't use anything but glass beads.

[enginedriver]

yeah, but the glass won't help keep the paint liquid unless you shake it.

why would the copper corrode? i don't think my paint will eat the pennies.

[Ritual]

Copper corrode because of an electro-chemical reaction.

[Henrix]

The problem wasn't that the coin corroded away, on the contrary, when I had cleaned the paint of the coin it looked sparkling new. So the coin not only corroded, but the paint solved the protective green corrosion layer that usually forms on copper.

The problem was that a glut of corroded copper and paint formed around the coin, and that the rest of the paint got grainy and weird.
I take it to be a detrimental effect of the solved copper salts.

It took a while before I noticed the effect. I don't remember exactly, perhaps a year or two.
The paints with copper coins all went bad, IIRC. The ones with bits of pewter/lead weren't so bad, but I could see signs of corrosion on the metal, so I stopped using any metal.

I remember Ral Parhta paints among those that were destroyed, and probably some of the old GW flip-tops. Probably others as well, but those were the ones I had most of at the time.

[Henrix]

i read somewhere (maybe in the White Dwarf) that putting pennies in your bottles of paint will keep them from drying out - something in the copper, i think,

If this is true it is a sign that the paint is somehow reacting with the copper coin, i.e. prbably some form of corrosion.

[Ritual]

Since coins consists of alloys you will have different metals present. Two different metals in an electrically conductive fluid is a galvanic cell. That means that one of the metals will be gradually corroded and the other metal will get a crust of metallic salt (from the corroded metal). Roughly speaking, of course... :)

[Duende]

I just asked our company's chemist about it and he has no idea how copper would effect the properties of paint (as mentioned in the first post). Without knowing the chemicals in the paint, he thought maybe the copper was reacting with any cadnium or lead in the paint (which could be possible for older paints). But he has no idea how copper would effect drying times, so I doubt a copper palette would make any significant difference there.

Just my thoughts. Anybody know where I can find out the chemical ingrdients of paints (esp the ones we use, not like house or furniture paint)?

[Henrix]

Well, I'm fairly certain that there were no cadmium or lead in the paints. Most manufacturers had shied away from those already, even though they were still legal.

The miniature paints today are almost universally acrylic paints, i.e. acrylic polymer, oftentimes with other chemicals to enhance the flow and whatnot, and a very wide array of different pigments, many of them metals or compounds including metals, like titanium oxide or indigo. (And water, naturally.)

So there is no simple answer to what paint contains.

[supervike]

Copper definitely corrodes...most telephone and communications lines are still made from copper...and if it didn't corrode and break down, I'd be out of a job!

As for a palatte made of copper...it seems to me, ANY metal under hot lights would start to heat up, making your paint dry even quicker...I'd stick with a cool white surface like a glossed ceramic tile or a plastic one.