Coloring cast bronze red

[novabelgica]

For one of my solar system sculptures, Mars to be exact, I need to find a chemical mixture to turn the cast bronze sphere red. The patina's I've tried have resulted in either a light orange or dark purple color. However, I need a rich, dark red.

Does anybody know of a mixture which would achieve this?

I'm using RG7 bronze by the way.

And since we're on this topic. I also need a mixture for white or light grey.

Any help would be immensely appreciated.

Thanks.

[rderr.com]

tinture d'ioide on a heated surface.

Robert

[rderr.com]

for the white or light grey try peau de taupe shoe polish. It will be slightly green to silver.

[fritchie]

Originally Posted by novabelgica

For one of my solar system sculptures, Mars to be exact, I need to find a chemical mixture to turn the cast bronze sphere red. The patina's I've tried have resulted in either a light orange or dark purple color. However, I need a rich, dark red.

Does anybody know of a mixture which would achieve this?

I'm using RG7 bronze by the way.

And since we're on this topic. I also need a mixture for white or light grey.

Any help would be immensely appreciated.

Thanks.

I believe some cadmium salts, possibly sulfides or selenides, are red (probably the same pigments used in cadmium red or cadmium orange paints). Heavy metals such as cadmium have a reputation for toxicity, though, so I’m not sure that is the best route. Ferric nitrate is said to produce reds on bronze, though I have not gotten this effect. (Exact temperature and application are said to be important.)

Various silver and bismuth salts are said to produce gray or white.

Have you looked at Ron Young’s books on patinas? He has one or more, with detailed formulas and excellent pictures. I looked at what probably is his first book about ten years ago, but I settled on a couple of simple and durable materials.

[novabelgica]

Thanks for the input.

Robert, I tried tinture d'ioide, but unfortunatley didn't get any result.

Fritchie, I haven't tried ferric nitrate yet, so that will be my next course of action. I have a (quite large) book on patinas, but none of the recepies for red have actually produced red. All I get is a light orange or purple color. Maybe it has to do with the bronze itself. The recepies are for LG bronze, and I'm using RG bronze, though I'm not sure what the difference is exactly. Anybody know?

I'm not ready to give up yet though.

[rderr.com]

After treating the sand blasted surface with livers of sulfer, cold, then rinsed, heat with a torch and apply tinture d'iode, in the open. I've a friend that does all his patination with diluted acrylics and heat, then hot waxed.

[fritchie]

You're off to a great start, Tim! The use of three different materials, as well as the craftsmanship and originality, make this very impressive.

By the way, how’s the search going for red and silver/gray patinas? When I mentioned cadmium selenide or other pigments similar to those used in artists’ Cadmium Red and Cadmium Orange, together with a warning about possible health concerns, I more or less expected you to hold off on them, but in the back of my mind I foresaw the possibility of plating the sculpture with metallic cadmium and then treating it with sulfide or selenide the way bronze is treated with liver of sulfur.

Later, it occurred to me that some or all of these red-painted steel sculptures might use the same or similar pigments, and they might pose the same hazards. I expect the typical patina process would give brighter, cleaner colors than paint, because no carrier body is present, but at the same time, the carrier (binder) might reduce potential hazard. Out of curiosity, do any of you who use these paints know the constitution of the pigment? (And you always could clear-coat a patina to achieve some degree of environmental isolation.)

[novabelgica]

Fritchie, thank you for the nice comment. We'll be installing the 'Sun' sculpture on thursday and friday, so I'll post a pic when that's done.

I'm still trying to find a decent red patina. I don't dare using cadmium, especially since some of the cities I'm working with already freaked out when they heard the Cor-Ten steel will come in contact with the earth. What, like a little rust is going to kill all life in a 3 mile radius? Please.

So the quest for a red patina continues.

[jwebb]

Here's a Red patina I came across in a book called The Complete Metalsmith by Tim McCreight. It's a "traditional Japanese patina", but I've personally never used it or seen it. The formula is 5 gm 'rokusho' and 5 gm copper sulfate to 1 liter of water. "Rokusho", in turn is defined as 3 parts copper acetate, 1 part sodium hydroxide, and 1 part calcium carbonate. This supposedly reddens copper or brass, so I would guess it should give a good result on bronze. The directions are "Immerse the cleaned workpiece in a boiling solution for at least an hour. When the desired color is achieved, remove and rinse in cold water." The book cited in turn credits another book for this recipe: The Colouring, Bronzing and Patination of Metals, by Hughes and Rowe. If you can give this a try please let us know how it comes out.

[novabelgica]

Jwebb, I have the book that you mention (The Colouring, Bronzing and Patination of Metals, by Hughes and Rowe) and I have tried a couple of their patina's, but not with the desired effect.

Here's one that I tried:

120 gm Copper Sulphate, 30 cm3 Ammonia in 1 liter of water. Boiling immersion for 20 minutes. This one turned out a light orange instead of red.

The most basic recipe: boling emersion in 25 gm of Copper Sulphate in 1 liter of water didn't produce any coloring at all.

The tinture d'Iode that Robert suggested didn't have the desired result either.

The main problem I have is that I do not have the time to try all the patina's and finding the ingredients is problematic since I often have to buy large quantities of a product.

But thank you for the patina you mentioned. I will see if I can find the ingredients and try it.

Maybe we should continue this conversation in the 'Community Help Center' where I started this topic? (looks at the moderators)

[your wish is my command, the 3 above posts moved here - Araich]

[jwebb]

Well, good luck, and, by the way, just in case you don't know it though you obviously know more than I, watch out for Sodium Hydroxide (NaOH). We use it in large quantities to dissolve shell material, and it'll burn flesh severely.

[fritchie]

Tim - I'm not surprised by these reactions to cadmium, though I am to Cor-Ten, and I’d still like to know the ingredients in the red paint used in all those large steel installations. All too often we fear the goblin we don’t know while living comfortable with the devil we do know. Just look at cigarettes.

And jwebb is right about sodium hydroxide, especially if hot. It can remove the skin when concentrated or on prolonged exposure.

[novabelgica]

Araich, thanks for moving the posts here. I didn't actually notice that you were the moderator for this section. Sorry about that. Didn't mean to boss you around.

Jwebb, I'm always careful with chemicals. Unlike some people I work with, who occasionally wonder why there's suddenly so many holes in their clothes.

Fritchie, can't help you with the paint question. I have no idea. Sorry.