Brass Patina Recipe?

[Mal Paso]

The mold below has cast well over 20,000 Boolits. I've have had to clean Alloy off the blocks twice. So far I haven't rounded any corners but I worry. Even with careful operation I've had Tinning on the underside of the crimp ring near the block faces and the the tips of the grooves on the block faces (503 Clone less than 2% Tin). I was getting small tearouts at the part line and boolits weren't dropping like they should. I carefully cleaned the mold and spent a day treating the blocks with Liver of Sulfur. It was slow and I would have gone for a darker (and more uniform) brown. A a couple thousand Boolits now and no tinning. It did change the thermal characteristics. The brass doesn't suck the heat out of the lead as fast and I'm running the pot 30 degrees hotter (680F) to keep the mold hot enough, but a fair trade for the Teflon finish.

I like the results but I'm sure it could be done better. Anybody have a better patina process for brass?

[quasi]

so you normally cast at 650 degrees?

[Maven]

Mal, If you use black powder in cartridges or ML's and clean with water, save the black, smelly resulting solution to immerse your mold blocks in. It will give them a "patina" in no time, especially if said solution is warm.

[geargnasher]

GENIOUS! I've been using the heat method, including a dusting with a very high-oxygen flame to induce an oxide coating on my brass moulds. I, too, cast with alloy at only about a hundred degrees above full-liquidus, which usually is around 700F or less, and still experience some tinning due to keeping the mould what is probably too hot for the tin not to accumulate.

Oxide coatings work really well for aluminum, I anodized a Lee mould recently and it is like a Teflon-coated skillet as far as lead alloy is concerned.

Recently I bought a bottle of Birchwood-Casey aluminum black (which is supposed to be pretty lousy as a durable finish) for the purpose of more easily treating aluminum with a non-stick coating. Haven't tried that one yet.

I helped a friend of mine "antique" some antique bath fixtures that were badly corroded. We cleaned them in a citric acid solution and then treated with a liquid product he found on-line somewhere, I'll have to ask him what it was. Worked very well for appearance, anyway.

Gear

[Mal Paso]

so you normally cast at 650 degrees?

I was at 650F (now 680F 95/3/2) with the #503 and the blocks just heat cycled to get some patina. This is out of a PID controlled Lee 4-20 Pot and Nothing goes back in the pot during the casting session. At 3 to 4 casts a minute there isn't time. I also have the PID sensor 5/8 of an inch from the pour valve. Mold goes in a Hot Plate Oven anytime casting stops.

This is my first brass mold and I first broke it in by heat cycling with the blocks closed not understanding that getting oxygen to the brass is important.

Gear, it was your experiments in anodizing that got me thinking about patina and helped me figure out why the heat requirements of the brass mold changed so much after treatment.

I used Liver of Sulfur from the local jewelry supply . A grape sizes chunk dissolved in a cup of hot water. It's likely the good quality of Miha's brass but what would have taken minutes with copper or silver took a day to achieve with brass. I'm sure there's a better formula.

Finely machined new brass molds are beautiful but problematic. I asked Miha if he would do a patina and he said it would add to the cost suggesting heat cycling. I would be willing to pay extra but it might be a complication he doesn't need.

[Mal Paso]

Mal, If you use black powder in cartridges or ML's and clean with water, save the black, smelly resulting solution to immerse your mold blocks in. It will give them a "patina" in no time, especially if said solution is warm.

Just realized, that was pretty close to what I used. Liver of Sulfur is Sulfurated Potash. No BP. Cost me $7.40 for an ounce. They also had 4 ounces of Liver of Sulfur for $11. It has a limited shelf life so buy only what you will use in a couple months.

[Dannix]

I may have to try this on a new Miha brass mould. Thanks for posting.

[JonB_in_Glencoe]

I've have had to clean Alloy off the blocks twice. So far I haven't rounded any corners but I worry. Even with careful operation I've had Tinning on the underside of the crimp ring near the block faces and the the tips of the grooves on the block faces (503 Clone less than 2% Tin). I was getting small tearouts at the part line and boolits weren't dropping like they should. I carefully cleaned the mold and spent a day treating the blocks with Liver of Sulfur.

OK,
How do you remove the "tinned" lead alloy spots off a Brass mold face ?
maybe Heat mold to casting temp, then use a brass brush ?

I like the idea of patina and using the used cleaning solution from a BP shooting session.
Jon

[Maven]

"How do you remove the "tinned" lead alloy spots off a Brass mold face?
Maybe heat mold to casting temp, then use a brass brush?"

Jon, You've got it partially right. Bring the mold up tp casting temp., then use a sharpened wooden dowel, cuticle stick, or something similar with a dab of NRA 50-50 bullet lube, etc. on it. Rub it on the tinned area to remove it. You have to remove the lube residue though. Btw, this is joeb's (Joe Brennan) idea.

[Von Dingo]

I've used Brownells oxhpo blue (spelling?) to antique brass. It has a sulpher smell, and darkens brass, unfortunatly I'm not more of a chemestry guy.

[Mal Paso]

OK,
How do you remove the "tinned" lead alloy spots off a Brass mold face ?
maybe Heat mold to casting temp, then use a brass brush ?

I like the idea of patina and using the used cleaning solution from a BP shooting session.
Jon

Warm molds are easier to clean. Beeswax really helps lift the lead. Small brass and Oak shapes were used as picks and scrapers. Bronze Wool from Brownells. And 0000 Steel Wool wrapped around wood picks to get the last bit off the crimp groove.

The tips of the mold in close proximity to the lead that can't dissipate heat fast enough are the problem areas. The Brass Oxide seem to insulate as well inhibit the Alloy's ability to attach.

[JonB_in_Glencoe]

Thanks for the hints.
here is my AM 41 WC
you ain't kiddin' about the "tips" area being problematic

[Mal Paso]

Use a wood or brass pick on the outside edge (away from the cavity) of the lead dots along with heat and beeswax. Brazing Rod sanded at a sharp angle works well. Some of them will lift off.

You need some Color on that mold.

[454gene]

How hot and how many times should you run your molds through this cycle?

[Old Caster]

Use one of the electric bore cleaners to clean lead residue from either a brass or iron mold . No damage to the mold, it is easy, and completely clean.

[Mal Paso]

How hot and how many times should you run your molds through this cycle?

If you can wait a couple days, I remembered, I have an old friend at the Monterey Sculpture Center who would know exactly what to do. Here's what I did.

I started with boiling water poured into a glass dish. Crushing the chunks helps dissolve the Liver of Sulfur. Heating the mold blocks in a 200F oven would help the heat loss. Dipping works faster than total immersion. The reason the lower part of the blocs is darker is, to keep the pins out of the solution, that was the water line and the darker portion was in the Air. I dinked around with it all day drying the mold on the mold warming hotplate between soaking sessions.

Preclean with Chemtool or other zero residue cleaner (Not Brake Cleaner). Any contaminate will cause uneven oxidation.

[Bagdadjoe]

Glad I read this before using my mold. I used to do stained glass and you can get a bottle of antiqueing solution that creates a patina on lead or brass. Also, to remove lead there is a "desoldering" wire you can buy that you get the solder to temp and it wicks the solder up off the joint. It's a very fine little cable made with multiple hair sized strands of copper. Might work on a mold? May be that you could use a soldering iron with the desoldering stuff between the tip of the iron and the mold and I'm guessing you'd need some liquid flux (also sold at stained glass suppliers) so that the lead would flow to the copper. I'm out of the business now so unfortunately I don't have the stuff to try. Everytime I sell something I need it later...and my wife wonders why I'm a "packrat"????

[Mal Paso]

Everytime I sell something I need it later...

I think it's one of The Rules of The universe.

Heating the Alloy to desoldering temperature would likely cause some of the Alloy to attach to the mold even better. Casting Temperature approaches soldering temperature but not enough for it to really "wet" the brass. I wouldn't take the mold blocks over 400F to remove the Alloy.

Liver on Sulfur works but the amount of treatment that would turn Copper Black turns Miha's brass slightly brown. I am trying to locate an old friend and sculpture caster who would know what to do with a tough project.

[Mal Paso]

The build up on the block faces is fairly obvious. What I didn't see at first was the tinning on the underside of the Lube and Crimp Rings right at the block faces. These small patches of Alloy were causing the boolits to hang and caused small tearouts at the part line. I lapped one mold which helped but the problem came right back. Careful inspection with a 10X Loop uncovered the real problem. I think those points of the mold don't have as good a heat conduction to the mass of the mold and overheat. Oxidation should insulate the mold a little in addition to the nonstick qualities.

[longbow]

Oddly, I have never had a problem with boolit alloy tinning to brass moulds. I thought it would be a problem but after I got my first Mihec mould, I didn't have any trouble at all and I tend to run things hot.

I only have two commercial brass moulds but several homemade moulds with brass nose forms and again, I have had no trouble at all.

In the past I have lapped iron moulds then accidentally overdone the preheating before casting and gotten the mould past the alloy melting temperature which resulted in some tinning on the shiny lapped portion of the mould but re-heating to just past the alloy melting point then wiping with a paper towel, scraping with a toothpick of bamboo skewer or other wood piece/dowel has removed the lead easily. After a bit of casting with those they heat blue and problem gone.

Heating to just over the alloy melting temperature should work fine for a brass mould too. I would try that then wipe with a paper towel to remove the lead in the photo in post #12. Application of Bullplate or other mould lube after would be a good idea then wipe clean and let the rest "cook" off during casting.

One point about the preheating of brass moulds is that apparently they can warp if overheated so that is something to be careful of.

As for a patina recipe if you want one, I would be looking at very mild solutions that will corrode brass. I don't know for sure but I suspect that just table salt in water would provide enough "corrosion" to help.

I would be very careful about applying anything to produce a patina though as you could end up with a pitted mould or rounded edges. "Sharp" bits tend to dissolve easily in corrosive solutions.

Longbow