Bronze Powders and exterior applications?

[Kelly Thorson]

Is there any way bronze powders can be used for any exterior applications? Will they tarnish if in a resin carrier? Will clear coat prevent tarnishing?
Are aluminum based powders less prone to tarnishing?
I've found a resin/powder combination I really like the appearance of, but don't know if I can trust it enough to use it for exterior use. The powder settles in the resin so none is on the surface.

[Danny Baronian]

All metal powders will oxidize or tarnish over time regardless of the carrier or coating. Same goes for any metallic paints which also contain metal powders. Aluminum powders are less likely to tarnish, but brass, bronze and gold colors are generally made from a mix of fine particles of brass, copper and zinc. Pure aluminum makes up the silver colors.

Last year we made moulds for columns that were to be cast with bronze metallic powders. The final castings had a 1 1/2" wall thickness. Within six months they had a nice patina as though it was a solid bronze casting. The carrier was a clear modified polyurethane resin. One of the final steps was to lightly sandblast the columns to expose the metal. At that point it was hard to distinguish between the composite and real bronze. A similar method and treatment is done with Luminore.

You can flash gild with mica powders that contain no metals and will not discolor. Sepp Leaf carries a large selection and are great people to deal with.

Another material to check out is aqua leaf by Ronan. They have quite a selection of colors, have brilliant looking metallics, and as I understand, are colored with mica powder or a similar material that will not discolor.

I was going to try the aqua leaf but it was a new product,expensive and untested.

[Kelly Thorson]

Thanks Danny,
When you say tarnish are you reffering to just losing some of their brilliance or are you talking turning black. I think an aging patina would be totally in line and even desireable in this instance, on the other hand turning black wouldn't. Being encased in a resin will the tarnishing be minimized? Does the fact the powders are such fine particles speed up tarnishing?
Sorry for the persistance, I'm dealing with a sign that has to be done for Christmas and the options in rural Sask on short notice are extremely limited. I can always resort to metalic 1-Shot if I need to, but this finish is so much nicer.

[Danny Baronian]

Composite metals, ie copper, zinc brass and aluminum will tarnish, and will not develop a nice patina. It will not look pretty in a month or two. Using 1 shot will do the same, as with any metallic paint as they all contain similar composite metals. The only one that won't discolor - by the manufactures claims - is aqua leaf by Ronan.

Do this for your own information. Paint some samples with 1 shot metallic, another one with Rustolium metallic or whatever your local supply stocks. Mix some composite metal into varnish and coat another sample. Date the back, stick it outside and check them over the next six months. I've done this for a long time, and know when I use a tested product I won't get a call back. Unless they order more.

The castings I spoke of used real atomized bronze, therefore developed a patina unlike composite powders.
One thing that may be causing confusion - metal powders that are generally used in signmaking are composites that are treated to look like various metals, but actually contain very little of the true base metal, if any at all. Brass, copper, nickel and bronze can be purchased in powdered and atomized form, but prices are considerably more and not a common product in many areas.

Real metal powders can be purchased from Douglas & Sturgess in San Francisco. Mike posted a supplier based in LA for composite powders and has the address and info on the supply page. Cres-lite is another manufacture of pigmented metallic colors, carried by sign suppliers as well as Dick Blick.

Composite powders encased in resin will slow the tarnishing to a degree, but it will eventually turn dark unless completely protected inside away from UV.

Another thing to consider is to leaf the project with dutch metal and clear it. That will hold up better than the powders.

Edit:

After reading the Cres-lite color chart, I read this notice on the back:

These metallic shades are produced with aniline dyes which are NOT light fast. Their use where exposure to ultra violet light may occur is NOT RECOMMENDED!

[Kelly Thorson]

Okay, I think what I have are real bronze powders. They have a "satin" lustre to them and lack the "glitzy" look of the cheaper versions, and I paid $8 for a little 10g vial. Or perhaps it is just expensive compound metal. I'll do some outdoor testing for future use. I have used the Douglas and Sturgess atomized powders for cold casting. I found them to have good service, support and pricing.

This go round 1-shot and mica will have to suffice.

Thanks for taking the time to explain.