Cleaning a Brass Mold and ...............

[Mal Paso]

I've found what I think is a safe way to clean a brass mold. I bought one of those $30 infrared thermometers which seems to be quite accurate on non shiny objects. I stripped the molds of protruding hardware and laid them flat on a piece of 3/16 steel. Using a medium flame I brought them up to 600F. I used a wood stick to hold them down and wiped the lead off with a cotton swab. A half drop of Sprue Lube or Beeswax helped the tough spots but only cotton was used for scrubbing. Shut off the heat and cool slowly. Like new, no warping.

BUT I'm still getting tinning on my mold. I'm beginning to wonder if it isn't the Alloy and will try some Rotometals #2 Alloy next. The second picture is after 200 casts. Alloy of 96/2.5/1.5 (from range scrap and locally formulated Lyman #2) was PID controlled at 650F. The MP 432256 was preheated to less than operating temp. 3 casts a minute, cut the sprue just after solidifying. Perfect fillout but the boolit wants to hang on the deposits at the end of the bands (blue arrows) And the first cavity filled has a deposit on the sprue cutter side of the top band Only.

This is my favorite mold so I'm open to spells or incantations.:wink:

[runfiverun]

nevermind the tinning where the arrows are look at it on the base band.
when you get some burnishing [oxidation] in the mold cavity's the tinning will stop.
if your alloy really is that much higher in tin than antimony you'll get tinning everywhere not just the mold.

[btroj]

Would some sort of brass black stop that? Sort of a super tarnish?

[dragon813gt]

Yeah, the base of the bullet in the block is tinned. I've never had that happen. The tinning on the face of the mold blocks is something I've learned to live with. It doesn't seem to effect anything unless it builds up to much which prevents the blocks from completely closing.

[HDS]

Yeah I get some small bits of tin near the edges (nothing like that though) but they don't affect function that I can tell. My .22 mold was the worst in this regard.

[JonB_in_Glencoe]

Gee, didn't you patina that mold ?
http://castboolits.gunloads.com/showthread.php?169575-Brass-Patina-Recipe&highlight=
because it sure looks alot less patina'd in your current photo.

I haven't cast thousands of boolits from the molds that I patina'd, it was three casting sessions and have NOT had the tinning reoccur.

I have no new ideas for you, sorry.

[Mal Paso]

I have 2 of the molds as it's the most accurate boolit I have. The one I showed in this thread only has a few thousand casts on it. I ran both molds this weekend and the Patina one did the same thing. I have a second pot I'll fill with certified #2 and try that. I've been working off the same blend (1200 lbs) since I noticed the problem.

My big worry was cleaning. 600F, done gently, doesn't seem to be a problem for my molds so I'll heat em up and wipe em off and try again. Using tools to remove the lead worried me.

I've got a 1100 cast and sized so the pressure is off for a month.

[quasi]

I have a MP 434 265 HP mould that I was opening to fast and got lead buildup between the pin bases and their recesses in the mould. It was tinned on, no amount of rubbing with a Tongue depressor while hot would remove it. Once cool, I applied some of the Bullplate type lube that comes with MP moulds, on the lead tinning, and let it sit for 4 or 5 minutes. I then rubbed the lead with some Bronze wool, and good by tinning.

[Michael J. Spangler]

i just went through a serous cleaning session with my MP 454-200HP

i stripped the mold down. then used a sheet of 1500 sandpaper on my surface plate, and took a couple passes to remove the tinning i had on both sides. (i'm sure some will throw holy water on me and freak out over that ; )
i then scrubbed the whole deal with copper glo and water paste. i guess copper glo is just salt and citric acid mostly.

i had some serious tinning on the top and bottom of the grease groove that needed to be dealt with. so i put a screw through a glue boolit and covered it with the copper glo paste. i put the glue boolit in the mold, closed the halves and spun the boolit by hand. worked beautifully to remove the tinning., except for the corners that had a couple big splotches.
i went at those carefully with the tip of a knife. once i got most of the big spots off i went back to the glue boolit to finish it up. the cavities look like new now.

then i took the tip of my knife and gently scraped out the vent lines. most of the gunk in the vent lines (i assume burnt sprue lube and such) scrubbed off easily with the copper glo, but where towards the top and bottom of the blocks the vent lines cross at about a 45 degree angle and i was no longer scrubbing in the direction of the lines. Thats where i needed to focus with the knife. a couple quick passes with the wet tip of a knife and the built up gunk just floated out.

once that was said and done (after about 45 minutes of gentle work) i soaked in the 2 parts vinegar to 1 part peroxide mixture for 15 minutes. That really cleaned up the mold blocks and gave them a nice golden color.

now i'm cycling them in the oven to build up a nice patina. Boy i wish i did that the first time. could have saved me a whole bunch of cleaning

i'm not a machinist but i do build custom knives and know a thing or two about finishing metal. the copper glo was a great cleaner for the mold. very gentle, and doesn't have anything abrasive enough to cause issues with wearing down corners or ovaling the cavities. well worth trying if you have a mess you need to clean up.

can't wait to see how these suckers look when they get out of the oven

[Mal Paso]

My MP 432-640 (hollowpoint) that I treated with vinegar and peroxide before heat treat stays very clean.

In an effort to keep the mold cleaner I did my last run (2,000) at 650F. Had to heat the Lee 4-20 spout with a Bic lighter each time I started a run but fillout was perfect. (Mold stays on a hotplate between runs.)

Funny but the Solid 432256 did not run as well at that temperature.

[Michael J. Spangler]

Hey mal.
Is that hotter than you normally run or cooler?
I try to run at 650 normally but It seemed with the 50/50 COWW and pure I had to run hotter to keep the spout from freezing.
I figure that, teamed up with some times not paying attention to melt temp was what caused the issue at first.

[geargnasher]

Quasi and Michael had ideas I haven't tried yet, might give those a go. The 'best' way I know how to get that tinning off is to make a Q-tip style swab out of fine bronze wool spun around the end of a split dowel and saturate it in mercury. A little gentle rubbing dissolves the tin/lead/antimony in short order. Mercury is of course highly poisonous and difficult to get, but two drops ought to do a whole mould and be safe if you take necessary precautions. The "tinning" in the corners of the cavities I think is mostly accumulated tin oxide from the surface skin of the boolits, so a certain reduction effect of any sort of oil (such as Bullplate) and some heat should convert the oxides to liquid, molten metal and be easily wiped away without the aid of mercury, just don't roast the blocks willy-nilly or they'll for sure warp on you.

Now I'm REALLY going to put my flame suit on for this part: To assist in break-in, patina formation, and generally reduce anxiety when casting with these expensive, often irreplaceable brass beauties, a light coat of soot from a butane lighter is your friend. Yes, I'm the smoke-hater, have preached against it for years, but it does help jump-start the break-in process without getting little seeds of alloy stuck right off the bat that cause gradual accumulation. One can also take some carbon black and dust the cavities with it via a camel-hair watercolor brush or cotton Q-tip to make the cavities resist tinning. I do this after cleanings and polishings, and with brand-new, mirror-bright moulds that tin really easily as soon as they get up to casting temperature.

Let me know when I can take off my asbestos suit....

Gear

[41 mag fan]

I got the fire extinguisher ready...just in case!

[geargnasher]

Thanks, Amigo!

Gear

[btroj]

I still wonder if some sort of chemical that creates a patina on the brass would help. Birch wood Casey used to make a "brass black", I think it would work quite well.

[Mal Paso]

No flames Gear, excellent post. I've noticed those tinning "seeds" and watched them get bigger.

The best patina I have produced was by stripping the surface Zinc and Lead molecules with the vinegar/peroxide solution before heat treating. That mold stays much cleaner. I think Miha's very fine brass does not like to tarnish.

Liver of Sulfur, the traditional oxidizer, by itself, wasn't as good.

Lead in the brass alloy is smeared across the surface during machining. That and the Zinc in the Brass Alloy impede oxidation..... I think..... Removing those exposes copper molecules which will oxidize.

Michael, I'm casting with 96% Lead/2.5% Antimony/1.5% Tin alloy and used to think 750F was the magic number. Adding PID Control, a hotplate and developing rhythm I have been dropping casting temperature but 650F with a hollowpoint mold is a new low. I was very frustrated with spout freezes when I first started. Part was the wild swings of the Lee Temp Control, the other was I didn't know how close I was to flowing lead. Literally 5 seconds with a Bic lighter is enough to bring the spout up the couple degrees it needs to flow. Don't put your hand under the spout, angle the flame or better use a BBQ lighter.

[geargnasher]

I flame-oxidized the cavities of a Miha mould once, I'll never do that again. With a 20x loupe it looked like the moon's surface, apparently I burned out the zink and it left the surface densely scattered with little dark pits. It still casts wonderfully, but looks like [insert colorful euphemism].

Gear

[btroj]

Flame oxidizing- out

I may need to see how my carbide lamp would do

[kbstenberg]

I must have been living under a rock. This is the first time I have heard of it. Other than Jon B's thread are there any other thread's that tell the whys and wherefore's of patinaing a mold? Kevin

[Michael J. Spangler]

i wish i had the mercury to clean my molds because i would use it for sure.
i was so fed up with my 2 cavity ideal 358156 last night that i ran a propane torch on it for about 5 minutes per mold half.
the lead flew off with a good bore brush scrubbing and after the mold cooled it was beautiful.
nice and clean, a dark color from the heat. i was happy. NO warpage either. the holes for the alignment pins were a bit peened on the opposite block that holds the pins. i lightly sanded that side of the block and now the mold closes better than ever.

boy i can't wait to cast with this sucker now! not to mention after casting about 800 with this mold the other night i now have a serious want for a NOE 360160SWC for sure. that looks like a boolit keith and ray thompson could both appreciate. swede got it right with that mold for sure

[Mal Paso]

I must have been living under a rock. This is the first time I have heard of it. Other than Jon B's thread are there any other thread's that tell the whys and wherefore's of patinaing a mold? Kevin

That was an idea I had to reduce the ability of Lead Alloy to stick to a Brass Mold (Tinning). Not everyone it appears has tinning problems but several of us do. I tried Liver of Sulfur which took a long time and had limited results. Then I stumbled on the vinegar/peroxide bath to prepare for heat treatment. I think it would be best to do it to a new mold. I think what Gear said about "seeds" of tinning get started is true and unless you get every speck of metal it comes back. My cleaning has had limited success. I'll try the Gear method next on one of the 432256s, then the bath, then heat treat to oxidize.

It may be that a commercial patina is the answer. The jeweler / sculpture patina recipes aren't strong enough. Brass isn't used for sculpture because it does not oxidize well or evenly. The commercial "Patinas" that I found so far for brass that produced a strong even color were really paint. I need to stop by the Monterey Sculpture Center and see what they say. I'll put the Birchwood Casey Product btroj mentioned on the shopping list too. They are one of the top metal finish manufacturers, not just guns.

[another gunslinger]

I have been helped by many threads on this fine site, but this one really saved my my sanity (and possibly a $120 mihec mold). I heated the mold halves in a cast iron skillet mold up and used a qtip soaked in sprue plate lube. Tinning vanished instantly!

One thing that has already been said, but I I have missed in my initial reading, is to warm the mold up to temp a couple times with the blocks OPEN. I disassembled the mold and put both in an old cast iron skillet, mold side up to warm a couple times to "tarnish" the brass. When I originally warmed the brand new mold up a couple times to break it in, it was was closed, probably why I got the the tinning in the first time, as the inside of the mold was hardly changed in color. After cleaning and warming again, the mold has has changed to a nice darker orangish color.