Brass Patina Recipe?

[Oreo]

Any chemical method needs to go from bright brass to castable patina without risk to the mold, and in less time then it takes to achieve the patina via heat cycling in order for the chemical method to be advantageous.

I was able to achieve a decent moderate patina in 6hrs by heat cycling my MP Molds on the electric hot-plate. I placed the molds directly on the hot plate, set the burner on high and walked away for an hour. Came back, turned burner off and walked away for an hour. Repeat twice more and done.

[Michael J. Spangler]

tagged.

i'm going to try some of the methods in this thread to remove the tinning on my brass mold.

[Oreo]

I removed a bit of tinning by setting the mold on the hot-plate on high which was hot enough to melt the lead. Then I just wiped the tin away with a wet rag. Same way you'd do with a soldering iron tip.

[fatelvis]

This may be a rudimentary question, but does applying a patina to the brass mould either by heat cycling or a chemical addition prevent tinning? And by tinning you're referring to slight amounts of lead being left between the blocks? I just bought my first brass Mihec mould, and havent casted with it yet. Thanks for clarifying things to a newby! Lol

[JonB_in_Glencoe]

This may be a rudimentary question, but does applying a patina to the brass mould either by heat cycling or a chemical addition prevent tinning? And by tinning you're referring to slight amounts of lead being left between the blocks? I just bought my first brass Mihec mould, and havent casted with it yet. Thanks for clarifying things to a newby! Lol

I believe so. If you've read through the whole thread, I tried a desolved BP solution,
I wish I would have only used the heat cycling technique.

[JIMinPHX]

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.

Please let us know how it works if/when you do get around to trying it. it sounds like a good idea to me.

Thanks,
Jim

[JIMinPHX]

Another option - commercial patina

I have not tried any of this on a mold before.

http://www.industrialmetalsupply.com/products/patinas
http://www.industrialmetalsupply.com...rt%20Flyer.pdf
http://www.industrialmetalsupply.com...0Universal.pdf

[Oreo]

I tell ya guys, just put the molds in a stainless pan cavity sides up, put the pan on the big burner, and crank the heat up high. Walk away for an hour then turn the heat off & let cool.

Rinse and repeat 2-3 times and done. Even after one cycle you can cast with those molds just fine.

Its so simple and easy I'll never mess with chemicals.

[MikeS]

Oreo: doing what you're suggesting is a good way to warp brass moulds! when I preheat a mould (brass or otherwise) on a hotplate I ALWAYS put a thermometer down into the mould cavities thru the sprue plate. I also preheat my moulds with the hot plate set on Medium which heats the mould to the proper temp for casting, and keeps it at that temp without much risk of overheating the mould (but I still always use a thermometer and keep an eye on the mould). Another advantage of using the medium setting rather than high is that if I put the mould on the hot plate on medium as well as turn on my lead pot at the same time, when the alloy is up to proper casting temp, the mould is ready too. Perhaps by using the high setting for heat cycling the mould it can be done slightly faster than heating it the way I normally do, but for me it's not worth the risk of warping the mould.

[Oreo]

Well, just my humble opinion but I get the impression the fear of warping molds is largely overblown. I'm not sure what it takes exactly to heat warp a mold but I haven't been able to do it this way and I've tried repeatedly.

I'd like to suggest that warping a mold has more to do with uneven heating then heat alone, at least with the temperatures achievable with an electric hot plate.

[MikeS]

Perhaps it's not as easy to warp a brass mould as some here have said, I've never warped a mould, but even so, is it really worth the risk of possibly warping an expensive custom mould when just a little bit of monitoring of the heating can prevent it?

[longbow]

While the mould warping issue is likely real, I am not sure just how much heat it takes and certainly don't want to warp one of my beautiful brass moulds by overheating it. Having said that, I have not had any trouble with tinning or casting in any of my 3 brass moulds. I am not sure why anyone worries about it. If you were to pre-heat a brand new perfectly clean mould to above the melting point of your alloy (especially if tin is added) then cast into it, I might see a concern about tinning but if the mould is cooler than the alloy (which it should be), the alloy should be freezing as it hits the mould.

Try soldering a piece of metal that isn't to the melting point of solder. Not easy to get the solder to flow. Lead alloy isn't solder and there is no flux on the mould either. I guess is some people are having trouble with tinning then they are doing something differently than I am.

In any case, all three of my moulds are still shiny, I have had no trouble with tinning and the moulds cast beautiful boolits.

To each his own.

Longbow

[Mal Paso]

My best result so far was to treat a clean mold in a mixture of 2 parts Vinegar to 1 part Hydrogen Peroxide at room temperature 15 - 20 minutes, until buttery gold color. Rinse with water. Then I heated the mold to normal preheat temperature on a hot plate cavities up and exposed to air for 4 hours. This Pic is halfway through the heat cycle.

[Mal Paso]

While the mould warping issue is likely real, I am not sure just how much heat it takes and certainly don't want to warp one of my beautiful brass moulds by overheating it. Having said that, I have not had any trouble with tinning or casting in any of my 3 brass moulds. I am not sure why anyone worries about it. If you were to pre-heat a brand new perfectly clean mould to above the melting point of your alloy (especially if tin is added) then cast into it, I might see a concern about tinning but if the mould is cooler than the alloy (which it should be), the alloy should be freezing as it hits the mould.

Try soldering a piece of metal that isn't to the melting point of solder. Not easy to get the solder to flow. Lead alloy isn't solder and there is no flux on the mould either. I guess is some people are having trouble with tinning then they are doing something differently than I am.

In any case, all three of my moulds are still shiny, I have had no trouble with tinning and the moulds cast beautiful boolits.

To each his own.

Longbow

The tinning I got was after many Thousands of boolits. The #503 is over 25,000 cast. The tips of the grooves at the block faces don't dissipate heat fast enough and do reach soldering temp. Patina gives me an edge there and the mold just runs cleaner. Lead wipes off. I cast at 660F, PID controlled sensor at the spout, 3 casts a minute and look for sharp edges on the bands.

[JIMinPHX]

by tinning you're referring to slight amounts of lead being left between the blocks?

Tinning is when the lead sticks to the brass. When you solder a piece of copper or brass & the solder flows across the base metal & sticks, that is tinning. You want to avoid tinning a brass mold. Once the lead attaches, it's going to be very hard to remove & your boolits will not drop out of the cavities at all.

When you solder, you add a type of flux to the base metal to help the tin/lead mixture stick to the base metal & flow across it. When you cast in a brass mold, you pour a clean alloy into the mold & do not use a wetting agent or flux because you do not want it to stick.

Tinning occurs most easily on clean base metal. An oxide layer, or "patina" helps to prevent tinning.

Also, when soldering, you heat the base metal to just above the melting point of the solder. When casting, you keep the mold a little below the melting point of the liquid alloy.

[Dannix]

My best result so far was to treat a clean mold in a mixture of 2 parts Vinegar to 1 part Hydrogen Peroxide at room temperature 15 - 20 minutes, until buttery gold color. Rinse with water. Then I heated the mold to normal preheat temperature on a hot plate cavities up and exposed to air for 4 hours. This Pic is halfway through the heat cycle.

Thanks, Mal.

I tell ya guys, just put the molds in a stainless pan cavity sides up, put the pan on the big burner, and crank the heat up high. Walk away for an hour then turn the heat off & let cool.

Do you have any idea on how high the temperature got?

From what I recall when I tried a heat-only approach, I PIDed my hotplate to [450F] or so and gave it many hours, but perhaps [450F] is simply way too low for it to oxidize properly. (I have a pretty serious Corning hot plate, so it would be imprudent to simply set it on high and walk away.)

Also, does this technique work better on a humid day?

[Mal Paso]

Excellent Jim!

I got no where near 700F. I would say 400F Max. You are just speeding up the reaction with oxygen in the air. You guys with electric cooking ovens, just put it in and cool slowly. The Vinegar/Peroxide removes surface lead and maybe zinc molecules protecting the copper from oxygen.

The tips of the grooves where they meet the block face have the worst path for dissipating heat. I have my melt as cool as I can and mold just hot enough for good fillout. What got me going on the patina thing was not tinning of the block faces (which I've had too) but 1/32" long patches on the underside of the grooves at the block edges. They act like wedges making the boolit hard to drop. You'll see little tearouts on the top of the bands at the part line. If I slowed casting speed and returned the mold to a hot plate each cast???? Na......

I got carried away with the 432640 in the picture above, the "finished box" is Full and I've got another 2,000 to size.

[Charlie Two Tracks]

I'm glad you guys posted on this. I have a post in "Our Town" about how I have been cleaning my mold each time I cast, for over two years, thinking it had to be shiny.

[TreeKiller]

Talked to a jeweler maker today that has been doing it for 40 years today and that worked with his dad that had been doing jewelry for about that long also. He said use liver of sulfur warm the mold till you cannot hang on to it. Have the sulfur solution warm paint it on with a brush and give it 3 or 4 squirts of 409. Buff it off and you are done. Going to try it on the outside of the mold first to see what kind of finish I will get.
Some of the things he made:
http://www.gaumers.com/?q=JGaumer_gallery

[Mal Paso]

Talked to a jeweler maker today that has been doing it for 40 years today and that worked with his dad that had been doing jewelry for about that long also. He said use liver of sulfur warm the mold till you cannot hang on to it. Have the sulfur solution warm paint it on with a brush and give it 3 or 4 squirts of 409. Buff it off and you are done. Going to try it on the outside of the mold first to see what kind of finish I will get.
Some of the things he made:
http://www.gaumers.com/?q=JGaumer_gallery

That is where I started in post 1. I spent a full day with a warm mold and Liver of Sulfur in boiling water from the tea pot. The effect wasn't strong enough, the tinning is back on the undersides of the grooves and I'll have to start over.

Miha, no doubt, uses high quality brass. I have a copper bar across the hotplate to set the mold on and it was Black after the first heat cycle. Monterey Sculpture Center just reopened and I'll try to get there this week.