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
http://i640.photobucket.com/albums/uu127/JonB_in_Glencoe/closeup-1.jpg

[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.[smilie=l:

[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

[Mal Paso]

I'm not looking for corrosion and have avoided chemicals that might produce that porous green finish or pitting of any kind. A couple household chemical recipes I tried produced green on cartridge brass. I'm looking the kind of brown oxide that protects old statues.

I suspect many molds have naturally oxidized past the point of tinning. I should have heat cycled my molds with blocks open before the first cast but I was overly careful. I really should have more molds too. That #503 has cast almost a half ton of lead.

[JonB_in_Glencoe]

I was going to wait til I got out and did some BP shooting to try using cleaning water as suggested by another member. BUT, what about just using black powder right from the can, disolved into water in a crockpot...non-metalic and provides heat. How much do you think ? 100 grains per half gallon of water ? or more ?
Jon

PS, why would you avoid soaking the allignment pins ?

[Mal Paso]

I was going to wait til I got out and did some BP shooting to try using cleaning water as suggested by another member. BUT, what about just using black powder right from the can, disolved into water in a crockpot...non-metalic and provides heat. How much do you think ? 100 grains per half gallon of water ? or more ?
Jon

PS, why would you avoid soaking the allignment pins ?

I have no idea how BP would work. Liver of Sulfur is easily available, not expensive, and has known results. I would experiment on scrap brass before trying it on a fine mold. Crockpot sounds like a good idea.

Pins? Liver of Sulfur also oxidizes Steel and I wanted to minimize that.

Longbow never had these problems and it may be that he was running his mold cooler. I started out running hotter Alloy and a cooler mold but I'm now casting at 680F. That's just enough to consistently get sharp edges on the bands. 3+ pours per minute.

Fascinating!

[Jailer]

What about a mix of vinegar and hydrogen peroxide?

http://brewingrabble.com/resources/surface-lead.htm

[ctious]

What about a mix of vinegar and hydrogen peroxide?

http://brewingrabble.com/resources/surface-lead.htm

That sounds like its more to clean the lead off the surface. Does not sound like it creates a protectivecoating

[longbow]

I run lead and mould hot with brass moulds. Hot being a relative term because I cast "by eye" ~ I have never used a thermometer. I usually pre-heat the mould until mould lube smokes a bit and I heat the lead until I get a slight golden tint on the surface then start casting.

I cast fast and steady until the sprue puddle takes too long to solidify then turn the heat down a little. So basically, I have the mould almost to melt temperature for a bit then turn the heat down so that the sprue puddle hardens in a few seconds after casting.

I have had several moulds beyond the melt temperature by over doing the preheat accidentally ~ not brass moulds so far but some home made moulds with brass nose forms.

Personally, I think that the preheating I do starts a bit of an oxide layer on the surface.

Also, I think anything that causes a patina is corroding the surface, maybe just a bit but after all bluing of steel is a corrosion process. What you don't want to do is get a solution that is too aggressive or selective. Brass has zinc and copper in it so some solutions can be selective and leach one or the other from the surface.

Not criticizing what you are doing, I understand that, but some reading this may decide to try something that is too aggressive and ruin a mould.

Longbow

[Jailer]

That sounds like its more to clean the lead off the surface. Does not sound like it creates a protective coating

I dunno, they say a picture is worth a thousand words.......

http://i19.photobucket.com/albums/b180/Jailer/Mold.jpg
http://i19.photobucket.com/albums/b180/Jailer/mold1.jpg

[Mal Paso]

Nice Tan! Much more even than mine.

[JonB_in_Glencoe]

Mal,
I'm thinking the Clean side is the side treated with the vinegar/hydrogen peroxide mix...not the patina'ed half. I am assuming the patina was from actual aging.

you can see the lead spots on the top of the "brown" mold half.
The Clean side has no lead spots on the top of the mold block and the actual aged patina is removed.

Correct me if I'm wrong Jailer.

The article by Brewer John Palmer (I've read his book about brewing, he has a Engineering/metalurgy Major) A very smart dude. Read the linked article, it explains
that the solution removes lead smeared onto the brass from the machining process and
brewers who use newly manufactured brass fitting would rather not have lead exposed to the wort/Beer.

[geargnasher]

A citric acid solution will passivate the surface and leave a very light patina.

Gear

[JonB_in_Glencoe]

Gear,
I did think of that. Do you think that "very light patina"/passivate would be enough to stop the tinning I got, as shown in the photo I previously posted ?
Jon

[Jailer]

Mal,
I'm thinking the Clean side is the side treated with the vinegar/hydrogen peroxide mix...not the patina'ed half. I am assuming the patina was from actual aging.

you can see the lead spots on the top of the "brown" mold half.
The Clean side has no lead spots on the top of the mold block and the actual aged patina is removed.

Correct me if I'm wrong Jailer.

The article by Brewer John Palmer (I've read his book about brewing, he has a Engineering/metalurgy Major) A very smart dude. Read the linked article, it explains
that the solution removes lead smeared onto the brass from the machining process and
brewers who use newly manufactured brass fitting would rather not have lead exposed to the wort/Beer.

The brown side is the side that was soaked. It started as a lead removal experiment that didn't work. The lead that was stuck on the mold didn't come off.

It was a dull golden color for a short time after it soaked and then eventually turned the darker brown that it is now.

[MakeMineA10mm]

Tagged for future referrence

[Dannix]

I'd like to thank everyone for this thread. I have tinning on a Miha 9mm brass mould, and this thread could not have come at a better time.

[Dannix]

I would be willing to pay extra but it might be a complication he doesn't need.
Yeah, that's likely true, but I would be willing to pay extra too.

Did you use all 4 ounces of Liver of Sulfur on this one mould? I have a mould tinned like JonB_in_Glencoe's, so I'm going to try to make patinaing a near future weekend's project.

I'm seeing "116 B-12 CHEMTOOL Carburetor/Cho​ke Cleaner" at $50. Is there any other, cheaper, "zero residue cleaner" option?

Also, to be clear, you left your sprue plate et al attached when you did this, but tried to avoid exposure for the alignment ? I ask because the sprue plate and stop seem patinaed as well.

Did you ever get in touch with your old sculpture caster friend?

[Dannix]

Nice results.

How long did you let it sit in the vinegar/hydrogen peroxide mix? At what temperature?

I presume you used a 2-to-1 ratio of 5% Acetic Acid (White Distilled
Vinegar) and 3% Hydrogen Peroxide, as discussed on the thread you linked?


I dunno, they say a picture is worth a thousand words.......

http://i19.photobucket.com/albums/b180/Jailer/Mold.jpg
http://i19.photobucket.com/albums/b180/Jailer/mold1.jpg

[williamwaco]

Patina:

I have used a propane torch to achieve this with recalcitrant iron and aluminum molds. (Never owned a brass mold - soon now. )

I use it only after all else fails but I have had good results with it.

.


.

[Mal Paso]

The brown side is the side that was soaked. It started as a lead removal experiment that didn't work. The lead that was stuck on the mold didn't come off.

It was a dull golden color for a short time after it soaked and then eventually turned the darker brown that it is now.

Have you cast with the mold yet? I cleaned up my 640 last night. The Alloy was mostly sintered to the brass and not fully bonded so easier to clean than the 503.

I think any removal of lead is going to be surface molecules and if the lead can be seen it's too thick to be dissolved by such a mild solution. If the visible lead is removed the solution may remove the microscopic lead that would impede the formation of oxide. Very Cool!

I knew I wanted the 432640 to be more oxidized before the first cast but wasn't sure about heat cycling with blocks open, didn't know how to patina, and Just Couldn't Wait. Need More Molds, More Calibers, More Patience! :cbpour:

[Jailer]

Nice results.

How long did you let it sit in the vinegar/hydrogen peroxide mix? At what temperature?

I presume you used a 2-to-1 ratio of 5% Acetic Acid (White Distilled
Vinegar) and 3% Hydrogen Peroxide, as discussed on the thread you linked?

Not long, maybe 5 minutes or so. It's been a while ago and I can't remember exactly how long I soaked it. The mixture was exactly as described in the link I posted.


Have you cast with the mold yet? I cleaned up my 640 last night. The Alloy was mostly sintered to the brass and not fully bonded so easier to clean than the 503.

I think any removal of lead is going to be surface molecules and if the lead can be seen it's too thick to be dissolved by such a mild solution. If the visible lead is removed the solution may remove the microscopic lead that would impede the formation of oxide. Very Cool!

I knew I wanted the 432640 to be more oxidized before the first cast but wasn't sure about heat cycling with blocks open, didn't know how to patina, and Just Couldn't Wait. Need More Molds, More Calibers, More Patience! :cbpour:

That mold is a mess. It was my first hollow point mold and one of the first molds I purchased when I started casting. Of course ignorance is bliss and I didn't set the mold up properly and I made an absolute mess of it. I still need to take it apart and clean it well and set it up properly. It does cast nicely and makes great bullets but needs some attention before I use it again.

[Reverend Recoil]

Ammonia will react will copper alloys to produce a finish from dull yellow, to a brown color, and to eventually a heavy crusty green coating. Artist looking for patina compounds that duplicate centuries of the aging of bronze sculpture may use something like liver of sulfur. I think liver of sulfur is ammonium sulfate. Ammonium sulfate is used to age the patina of new copper roof and gutter repairs to match the appearance of the original work. All us bullet casters need is a simple chemical that will passivate the surface of a brass mold so the molten lead will not wet( or tin) the surface. Any solution with ammonia will work such as ammonia based home cleaners or copper removing bore solvent. Do not soak the mold block in the ammonia or it will be spoiled by a thick green corrosive crust. Wipe the mold with a strong ammonia solution several times over a day or so until you get a dark brown patina.

[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/SharedContent/Documents/ProductLiterature/Sculpt%20Noveau%20Flowchart%20Flyer.pdf
http://www.industrialmetalsupply.com/SharedContent/Documents/ProductLiterature/Patinas%20Universal.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.

[Mal Paso]

Ok, so here is a picture. These are the 2 worst cavities. Nowhere else in the cavities is there significant lead except the bottom of the bands at the block face. The grey in the middle, top band, of the right cavity is light from a window. Most of the guys having no trouble are running higher alloy temps. I will try that as well as seeing if the lead will wipe off with a cloth rag once the blocks are heated.

I shot bunch of 429421s yesterday and don't think it's quite the boolit the MP 432256 is so I've got to get this figured.

[longbow]

I gotta say, I am baffled!

I run "hot" when casting with brass moulds and I have not had any tinning at all even in a brand new unbroken in mould.

Having said that, I normally cast wheelweights or range scrap and I add little if any tin ~ maybe a bit of 50/50 solder but usually none.

The only times I have ever had any tinning trouble at all is with iron/steel moulds I have lapped, not re-blued or heat blued then overheated at pre-heat and gotten then a little past the alloy melting temp... oops! In an extreme case, I have actually had to melt out a boolit. Then, yes I have had severe tinning but I just re-heat and wipe it off then let the mould cool down well below casting temperature then cast until it is back up to casting temperature. No more problem. After heat bluing no more tinning.

Oddly, I have not had the problem with brass moulds! Even new shiny clean brass.

Are you running high tin addition? If so then maybe that is the difference but even then with your patina I wouldn't have thought you would get trouble like that.

It certainly isn't that I didn't believe you, I just have never experienced any sort of problem like you are having. A picture is worth a thousand words!

Yes, if you carefully and even heat the mould up to the melting point of the alloy, you should be able to wipe the lead off with a rag or paper towel then let it cool down and cast to bring it back up to temperature.

No other suggestions.

Longbow

PS: One more thought just occurred to me. I seldom prep moulds for casting other than wiping them off with a paper towel or rag... even brand new moulds. I do not scrub with dishwashing liquid, soak in mineral spirits, spray with brake cleaner, etc. I simply wipe them off then preheat until they smoke (which is below the melting point of lead) then start casting. I seldom have many rejects and don't get tinning even in new moulds. Maybe the oils oxidize and leave a "varnish". I also oil all my moulds ~ yes, even brass and aluminum because the sprue plates are steel ~ when I store them.

[Mal Paso]

I'm casting at 660F with alloy just under 3% Antimony and less than 2% Tin. Don't use anything but a little Sprue Lube on the top and pins. It sounds counter intuitive but I will try hotter alloy and see what happens.

You can see how the boolits would hang up rather than falling out of the mold.

[Iron Mike Golf]

At one time you could get acid core solder for plumbing (not sure it still exists on the market). Is it possible there is residue from the vinegar acting as a fluxing agent?

[Mal Paso]

The mold was thoroughly washed in Distilled Water before the heat treat and the mold cast 3,000 boolits before the problem was even noticeable. I can't imagine a trace of any chemical in the cavities.

[longbow]

Mal Paso:

Just after I posted here, I saw another thread with the same problem using a Mihec brass mould!

Yet another thought occurred to me ~ you might try using a graphite or other mould release which should coat the brass and not allow tinning at all.

It is worth a try.

I am not sure I would try casting at higher temperature though since tinning will probably get worse. Heating the mould to remove the tinning, yes, but not casting hotter if you are getting fillout now anyway. Cooler would be better at least to the point that you cannot get good boolit fillout.

There may be something to what Iron Mike Golf says too. A mould release should fix that too if it is a problem.

I would figure with the oxide layer you have that tinning would be next to impossible! Think of intentionally trying to solder something with a layer of oxide like that on it! That would be a no go.

Sorry, that's all I've got.

Longbow

[Mal Paso]

I'm running the Alloy just hot enough to get good fillout. Even, sharp bands all the way around. It may be that the temperatures of mold and alloy are too close together. I you look close the deposits are nodules not continuous and wetted to the brass. More like Sintered metal.

Higher Alloy Temp might get me temperature differential with the mold.

The 432640 isn't having problems but it has a better patina and runs at a higher temperature.