Lead Adhearing to Mould

[ColColt]

Having a little problem getting rid of a very small piece of lead right at the second drive band on one half of the mould. I tried brushing it off with a cloth while still up to temperature and it didn't work. I tried a toothpick and the same. Being a brass mould I didn't want to try anything sharp for fear of scratching it. Any suggestions as it's leaving a mark on the bullets like there was trash in the mix when it's not, it's coming form this stuck on small piece of lead.

http://i180.photobucket.com/albums/x220/ColColt/Gun%20Related%20Stuff/_DEF4385h_zpsd689b6dd.jpg (http://s180.photobucket.com/user/ColColt/media/Gun%20Related%20Stuff/_DEF4385h_zpsd689b6dd.jpg.html)

[country gent]

Wash it with dishsoap and water then with a popcycle stick (Cut it to a square edge at an angle) lightly and gentle work the spot. You may want to warm it up close to temp and try this also. Bamboo skewers from the grocery store are handy to have for this also. Soap water may get between lead and metal loosening it. As a little heat may also break the bond

[HeavyMetal]

Thyink I'd try a good # 2 pencil with not to sharp a point and a brand new eraser on it!

Rub with both ends of the pencil and see what happens.

[longbow]

I would heat the mould to melt the lead... just melt the lead, then wipe out using a cloth or wooden stick as mentioned.

I see "staining" from lead in that cavity too and I have to wonder why some people seem to get this going on. There is a thread on adding a patina to brass moulds to stop it from happening and I can't figure out how it is happening to begin with.

I pre-heat my moulds until the sprue plate lube smokes then start casting. The mould is not much below the melting point of lead when oil smokes. Still, I have not had any tinning or lead sticking to my brass or iron moulds.

Not criticizing, just curious why some people seem to have the problem. Maybe too much tin addition?

Back to your problem, I would use a thermometer or oil just smoking to make sure the mould is right about lead melting temperature then use a wood stick to scrape that bit out.

Be careful not to overheat the mould as brass moulds can warp but heating to the temperature of molten lead should not do it any harm and the lead should come out easily then.

The more I think about it, I wonder if it is tin addition. What alloy are you running? If it doesn't have tin then that obviously isn't it.

Longbow

[ColColt]

Nothing seems to work so far. I've tried heating also with a torch, playing the flame back and forth and all around as not to play it too long in that cavity and it still refuses to budge. This is the first of three other brass moulds this has happened with.

The alloy is from RotoMetals, 1:20.

The problem it's creating is a small ding on the bullet on the second band, like it's been dropped. It also makes the bullet want to stay in the cavity and hard to release.

[bangerjim]

Well, it looks like you got some compound in there that "tinned" the brass and allowed the lead to stick, just like solder! That could be difficlut to remove. I have not experience with brass molds. Have only aluminum ones. I have always wondered what keeps the lead from "tinning" a spot or two in the cavities of brass molds. That would seem to me not to be a good choice for molds but everybody seems to love them.

Good luck!

bangerjim

[John Boy]

Try white vinegar mixed 50% with hydrogen peroxide

[ColColt]

Tried the vinegar/Peroxide and no dice. It did turn the lead(tin whatever it is) dark so you can see it better.

[freebullet]

As others said-rub yer wood on it.

[ColColt]

I've been doing that to no avail. It may be there for the long haul. Nothing seems to move it. If I had better eyes and a good magnifying glass I'd try picking it off with an Xacto knife.

[Heavy lead]

I did this with one of my beloved brass moulds, I was able to remove it by soaking it in kroil for about a week, heating it up then wiping off, popped right off with no issue.
Good Luck

[ColColt]

It appears I may need to try that. Nothing else has worked. It's like it's cemented. I don't recall having another mould do this before. But, that's a project for tomorrow.

[JonB_in_Glencoe]

beeswax

[ColColt]

Rubbed on and let sit while hot?

[JonB_in_Glencoe]

I had to search for the thread.
http://castboolits.gunloads.com/showthread.php?169575-Brass-Patina-Recipe&highlight=
Start at post #8 read through post #13
AND
read all the posts to learn about patina
Good Luck,
Jon

[ColColt]

I'll read that and thanks. I've heard of "patina" before but never read about it as it wasn't a concern.

[JonB_in_Glencoe]

Not criticizing, just curious why some people seem to have the problem. Maybe too much tin addition?
Yep, Not every brass mold does this. Mostly it's the lack of patina/oxidation on the surface...which I suspect is a factor of the actual Brass alloy, some alloys tarnish/oxidize easier than others, add to that the boolit design [is there lots of points?], then lastly would be the mold temp, and that depends on the alloy temp.

Brass molds usually beg to be run hot, which also adds to the potential problem.

I suppose a high tin content alloy may add to the problem, but honestly I'd never used anything higher than 5% and with my 41WC mold that I have posted photos of the tinning problems...that mold has only seen alloys with tin percentages of less than 3%, realistically I'd say 2% or less.
Jon

[longbow]

I have to think that your Rotometals 1:20 is to blame for the tinning. Not that there is anything wrong with the alloy, just that there is enough tin to "solder" to the brass.

I would go with heating to the melting point of lead and scrape off with a wood stick or rub with a cloth.

Alternately you might try casting very hot with a good mould pre-heat and cast with straight wheelweights for a bit. That may take the build up out.

I still think though that if you carefully heat until the lead is soft then it will wipe/scrape out. I would use an oven or hot plate not a torch. Maybe once the mould is near the melting temperature for lead a torch to provide that little extra at the glob.

Once it is out then you may want to try the artificial patina. I have to think that others with this tinning problem are using fairly high tin alloys. I use mostly range scrap and wheelwheights so that may explain why I have no problems with tinning in my brass moulds.

Longbow

[Springfield]

Seems to me if you have heated up the old hot enough to cast with and it still doesn't come out then maybe it isn't lead. I have never had this happen with any of my 12 Mihec brass moulds, but then I always preheat before I cast the first time.

[geargnasher]

Springfield is right, it isn't lead, or tin, that's why it won't melt away. It is accumulated oxides of mostly tin, it starts a 'seed' in a shiny spot and just builds and builds a few molecules at a time from the flash-oxidized molten surface of the metal you pour into the cavities. It's the same sort of stubborn crud that clings to the sides of a casting furnace as the alloy level drops. A reducant like beeswax or paraffin quickly takes care of it once you get the mould up to the melt point of the elemental metal.

Being an oxide, and beeswax being a reducant as JonBinGlencoe pointed out above, you can heat the mould to the point that the tin would start to melt if it weren't oxidized, apply the wax to instantly reduce the oxides to elemental, liquid metal, and wipe them away.

It happens to me with brass moulds because they do like to be run hot, it IS worse with binary lead/tin alloys, and the brass moulds DO like to be run hotter/faster than other types which DOES exacerbate the oxide accumulation.

What I do to patina a brass mould for the first session is preheat it to casting temp in a mould oven and let it cool naturally a few times, then smoke the cavities lightly with a BBQ grill lighter before ever putting lead in there. That keeps those little soldered "seeds" from ever starting. After a few casting sessions, I wipe out the soot and leave them alone. This is the only time I ever smoke moulds because it can cause a lot of other problems, but it really helps break-in with brass.

Gear

[billyb]

Try heating the mild up to casting temp. Take a stick of bullet lube and apply a small amount to the stuck on lead. Then run molten lead over the deposit, build a pile of lead up over the open cavity then pry it off with your pop cycle stick. You may need to try this a few times to get the stuck on lead off. Use a paper towel to wipe the loose spots off.

[quasi]

soak the spot with Bullplate sprue lube, after a few minutes rub it with a carved popsicle stick or better yet a chopstick. Problemo fixed.

[ColColt]

The beeswax did the trick. I heated it up on the hot plate, smeared a bit of beeswax over the offending area and let it sit just a little and took a small dowel rod and then tried a toothpick and it came off. That cavity is discolored now but as long as it still cast well, no matter. This is the first brass mould I've used the 1:20 MIX with. The other brass moulds are pistol moulds and with those I use ww's plus a couple ounces of tin or I'll mix an equivalent 50/50 lead to Linotype and add lead to give me a BHN11-12 or close. Never had this problem with those moulds. Obviously, the tin is the problem. Wish I had known this early on I would ordered an iron mould. Now, to keep this from happening again. In the future any mold I order for large cavity bullets destined to use 1:20 or 1:30 will be iron or aluminum.

That photo in post #12 is the worse I've seen. I'm sure glad this one wasn't that bad.

http://castboolits.gunloads.com/showthread.php?169575-Brass-Patina-Recipe&highlight

I located another thread about this problem.

http://castboolits.gunloads.com/showthread.php?204271-Cleaning-a-Brass-Mold-and&highlight=patina

[hiram]

Try rubbing with a bore brush that is screwed into a handle. Use it on a hot mold.

[Mal Paso]

Springfield is right, it isn't lead, or tin, that's why it won't melt away. It is accumulated oxides of mostly tin, it starts a 'seed' in a shiny spot and just builds and builds a few molecules at a time from the flash-oxidized molten surface of the metal you pour into the cavities. It's the same sort of stubborn crud that clings to the sides of a casting furnace as the alloy level drops. A reducant like beeswax or paraffin quickly takes care of it once you get the mould up to the melt point of the elemental metal.

Being an oxide, and beeswax being a reducant as JonBinGlencoe pointed out above, you can heat the mould to the point that the tin would start to melt if it weren't oxidized, apply the wax to instantly reduce the oxides to elemental, liquid metal, and wipe them away.

It happens to me with brass moulds because they do like to be run hot, it IS worse with binary lead/tin alloys, and the brass moulds DO like to be run hotter/faster than other types which DOES exacerbate the oxide accumulation.

What I do to patina a brass mould for the first session is preheat it to casting temp in a mould oven and let it cool naturally a few times, then smoke the cavities lightly with a BBQ grill lighter before ever putting lead in there. That keeps those little soldered "seeds" from ever starting. After a few casting sessions, I wipe out the soot and leave them alone. This is the only time I ever smoke moulds because it can cause a lot of other problems, but it really helps break-in with brass.

Gear

Excellent Post! I had not considered oxides. It certainly explains why the deposits are so tough and why beeswax works.

Curious though, what is the trigger, why that spot? The underside of the groove (as cast with base up) at the block face seems to be The Spot.

[ColColt]

Since I had the mould cleaned up from all that tin or oxides, whichever, I decided to cast some with it today. Had to pound on the handle pivot again but this time I noticed the deposits on the right half of the mould instead of the other side. Aggravated, I hit it with the beeswax stick and let it cook in and then took a wooden paint stick to it and they flicked right off. Went back to casting with little trouble after that other than the half dozen that were wrinkled due to the wax. Maybe sooner or later it'll stop this.

[Springfield]

All my brass moulds have worked fine, but then my Mantra is "tin is over-rated, use more heat!". A good casting cadence can solve many problems. That plus I don't clean my moulds all that much when new, especially the better quality NOE, BRP, Accurate and Mihec. I have on occasion done nothing to a Mihec mould except heat it up a couple times to burn off the oil, then cast. My moulds don't look nice and shiny but they are tools, not art, so I do what works the best. Lee moulds I do a bit of scraping off of chips and facing off the front of the sprue plate, and stake the pins in place, but not much clean-up except a quick bath with dish soap.

[Iron Mike Golf]

I have had the seeds, but wiped them off before they grew. Now I check before pre-heating the mold. I use equal parts Sb and Sn. 2-4%

[longbow]

What Springfield said ~ "tin is over-rated, use more heat!"

I seldom add any tin and then it is 50/50 solder bar. Usually, I simply flux regularly and cast fast and fairly hot to get fillout using mostly range scrap or wheelwheights. No tinning (or tin oxide or whatever) problem for me.

My boolits are usually slightly frosty and that suits me.

After some use a natural patina should form and protect the mould but an artificially produced patina could be the answer as Mal Paso was working on.

Longbow

[Mal Paso]

I don't think I've ever gone over 1 1/2% Tin and I"m the poster boy for tinning. I do confess to range scrap, fishing weights, and a local gunsmith's homemade Lyman #2.

My last run at 650F still tinned at The Spots.

I have a different batch of Alloy blended as well as Rotometals #2 and a few things to try when work slows.

[ColColt]

I've went through three heat/cool cycles. Next time I'm going to smoke those troublesome cavities. I'm casting big bullets at 750-770 degrees and don't have this trouble with iron moulds.

What I need right now is more lead! I think I'm down to 30 pounds with twice that in Isotope lead but don't know about the antimony content, if any, in that brew.

[35isit]

I have a LBT aluminum mold with the same problem. Will the beeswax trick take the solder out? Can I use some LBT blue lube to get it out?

[WILCO]

Well, it looks like you got some compound in there that "tinned" the brass and allowed the lead to stick, just like solder!

w0w!!! I never would've though of that Bangerjim! Thanks for throwing that out there.

[dragon813gt]

.
with twice that in Isotope lead but don't know about the antimony content, if any, in that brew.

Which ones, large cores, small containers or other. The large cores are 3% antimony and 1% tin.

[John Boy]

With beeswax doing the trick I believe that paraffin would work well also

[ColColt]

Which ones, large cores, small containers or other. The large cores are 3% antimony and 1% tin.

I don't know what they originally looked like as I got them in ingots some time back during a group buy. Last time I checked them with the Lee they were BHN10. I can't recall who had them for sale on the forum. It just came to me...Muddy Creek Sam, last June a year ago during a group buy.

[ColColt]

Oops...double post

[dragon813gt]

Should be between and two and three percent. The tin content will be higher if it's not from the large cores.

[ColColt]

Hmmmm...I was hoping no antimony as I wanted to use it for 1:20 alloy for BPCR loads .

[dragon813gt]

Unfortunately the common forms of isotope lead contain antimony. I use the large cores and dilute it down to two percent at most.

[ColColt]

I can always use it for the pistol loads. The search for some decently priced lead/tin goes on. I'm still amazed at the price of a pound of tin these days.

[leadman]

The isotope lead works great air cooled for handgun medium velocity loads and light rifle loads. Water quenched it works up to about 1,900 fps in my 30-06, usually about 15 BHN.
I also use it air cooled in my Pedersoli Rolling block in 40-65. Works great.
Cold bluing for guns will give brass gun parts a nice aged looking patina on them. Would this work on a brass mold?

I wonder what a soldering iron would do to these spots of oxide that build up?

[PbHurler]

Call me crazy, but there's alot of good information in this thread. Could this possibly be "stickied"?

Just my thoughts.

[ColColt]

I wonder what a soldering iron would do to these spots of oxide that build up?

Good idea. I'll try that when there's a next time...not if but when.

Since I have a fair amount of Isotope lead, I may as well try it since it's been sitting there for months begging to be liquified.

[another gunslinger]

+1 on the sticky. Saved my beautiful 308 mihec mold by warming it up and using his supplied sprue plate lube on a q-tip to easily remove all the tinning! Instantly! No scrubbing, no wood sticks, no damaged $120 mold!

[ColColt]

That's good news on your mould but what about next casting session? That's what I want to eliminate, not having it happen again.

[happy7]

I have had a lot of problems with this. Just for what it is worth, in addition to brass I have had problems with aluminum and iron , so it is not just brass. It only happens to me with alloys that had added tin, such as 1-20 and WW with added monotype.

[dudel]

How about using a foul-out? Get the lead out atom by atom with no scrubbing. Clip one lead to the sprue screw the other to the rod. Submerge in lead-out solution. Give it a few hours.

[Mal Paso]

I think brass molds run a lot cleaner if the brass is oxidized. I have some MP 503 clones in rotation and as they "tinned" and boolits started to hang I cleaned them and tried a new patina. The last one was a suggested by a member and it's the best yet.

Cleaning: MP molds are works of art and my goal was no dimensional change (including scratches from cleaning). I've had no warping from heating the mold halves, stripped of hardware, cavities up on a 3/16 steel plate sitting on a gas range burner. I have a HF Infrared thermometer and I don't let them go over 650F. At that temp most lead wipes off with a half drop of Sprue Lube on a long Q-tip. Beeswax and Popsicle sticks will get most of the tough spots. When it's down to molecules, after cooling slowly, I put the mold halves in a bath, 1 part Hydrogen Peroxide to 2 parts Vinegar for 15 minutes, clean, soak again. Seems to me I used M Pro 7 to get some black deposits off. That's to get a mold back to a pristine state.

I worked out the following out on one of my first 503s and was impressed so when HP mold arrived I only did one double check of my early work.

I stripped the mold of removable hardware and cleaned the mold halves with warm water, Dawn, and a tooth brush to remove oil. I rinsed in Reverse Osmosis Water because I could. The mold then went cavities up in a bath of 1 part Hydrogen Peroxide to 2 parts Vinegar at room temperature for 30 minutes. Washed in water (RO) and dried. I applied Birchwood Casy Brass Black with a 6" Q-tip to the mold cavities, top and block face. You can't put the swabs back into the bottle after they touch brass so I'd put in 6 in at a time and throw each away after use. It takes about 5 to cover each block. Rinse, dry, and repeat. Brass is Really Hard to Patina. Just keep putting Brass Black on the bright spots until it evens out. Took me about 8 applications until it looked like an old, polished, statue.

Birchwood Casy is big in metal finishes not just guns any they say no dimensional change.

I cast almost 600 last night, lead doesn't stick. I raised my casting temp to 675F and slowed down a bit, left the mold open longer for more temperature difference between alloy and mold. Cleanest run ever. The new HP MP 503 clone is awesome.

For me it looks like problem solved. For those who never had a problem with brass molds: Nevermind (GR)

[Dumasron]

"Lead Adhearing to Mould
Having a little problem getting rid of a very small piece of lead right at the second drive band on one half of the mould. I tried brushing it off with a cloth while still up to temperature and it didn't work. I tried a toothpick and the same. Being a brass mould I didn't want to try anything sharp for fear of scratching it. Any suggestions as it's leaving a mark on the bullets like there was trash in the mix when it's not, it's coming form this stuck on small piece of lead."
********************
My suggestion would be to take a piece of B/C lead cloth and rub out the offending flake. It works for me on the plain mould faces.

[chrissy4560]

use hoppies like you were cleaning your barrel, you may need to put some on a cotton ball and let it sit on it for a while... thats what i usually do

[chrissy4560]

what do you use to keep the bullets from sticking to the aluminum? i tryed smoking with all sorts of stuff, they still stick...

[Grump]

I remember from years ago that vinegar tends to dissolve rust. Black oxide on iron-bearing metals is fine rust...

Anyway, since my attempts with three different bore cleaners over the past year show that they work on lead so slowly as to be "maybe it don't work at all", I'm interested in a more proven chemical approach while avoiding electrolytic processes. I just can't get myself to WANT a Foul-Out machine...

So, how safe is the 1/3-Peroxide/2/3-white vinegar mix for iron moulds? Just got a misbehaving RCBS back from the maker and after two sessions I'm plagued with tiny pinprick lead goobers on parts of the mould, next to and sometimes IN the vent grooves.

I won't talk about base fins from a badly curved sprue plate that I spent maybe 90 minutes grinding flat on my diamond "stone"...

Have two other iron moulds that need a bit of cleaning, so any time/temperature curve limits on soaking them would be most useful.

Thanks!

[Mal Paso]

That peroxide mix corrodes Iron a bit during a short soak. Overnight could do damage.

Heat is better. Heat the molds on a hot plate above the lead melt point and wipe it off with a Cotton rag. Beeswax and Sprue Lube can help. Cool slowly.

[happy7]

What Mal Paso says works. Get the mold really hot so the lead on it is molten and then use a Q tip soaked liberally in Sprue Plate Lube, preferrably the blue stuff, and wipe it off. You only have few seconds if you remove the mold from the heat to do this, so it may take several heatings to get it all. If it doesn't wipe off, the mold isn't hot enough.

Keeping it from coming back is still the tricky part for me. I am experimenting with different things, but am not overly successful yet.

[Grump]

Thanks!

But okay, where do I get some sprue plate lube nowdays? I've gone to the BullShop web page a few times but it doesn't have any product ordering stuff I can locate.

Do I remember RandyRat offering some of that??? Almost halfway through the last batch of Loob I ordered from him...

[Toymaker]

A drop of Kroil over night will creep under the lead and you'll be able to pop it off with a toothpick or popsicle stick. Wash with soap and water, alcohol then acetone. Re-smoke or treat your mold if you do that. Works for me.
I treat with Rapine mold prep

http://www.dixiegunworks.com/product_info.php?products_id=8095&osCsid=dced

[Mal Paso]

I decided to move my mold cleaning from the kitchen stove to an electric hot plate to cut down possible lead contamination and make work more comfortable. It came up to temp quickly but after a bit I had to fiddle with it to maintain temperature. I have PID control for both my pots so I looked to see how cheap I could build another PID. I found a MYPIN control, thermocouple and 25A SSR on Amazon for $41. The 6x6x4 box from an electrical supply was $10. The cords and switch already I had. Shoulda spent the extra couple bucks for a TC plug and socket. Oh well.

My Auber equipment is definitely better quality. The MYPIN thermocouple nut actually broke but I managed to get it all running in a few hours. The thermocouple is screwed into a boss that was braised to the bottom of the steel plate sitting on top of the heating coil. The temperature is bracketing my IR thermometer and after auto tune it works very well. I left the Hot Plate control alone as it works fine set to HI.

There is also a can that fits over the top for mold preheating.

[Mal Paso]

Here's my setup. Stick to hold the mold from moving. Cotton swabs do most of the cleaning. I drop a tiny flake of beeswax on the plate, quickly soak it up with the swab and clean. Sprue plate lube works too but not as well with oxidized lead. The other tool is a drill bit holder with a Brass Dremel Brush for the tough spots. I used to wear gloves but this unit doesn't radiate excess heat like the burner did.

Edit: Geargnasher suggested and I agree the difficult spots that don't melt when they should are oxides. Beeswax acts as a reducer. Once it is base metal again it should wipe off.

OH, and a Big Lighted Magnifier so I can see what I'm doing.

Notes: The steel plate is transferring heat to the mold and needs to be set higher than the temp I want the mold to be. Right now it's 700F + to clean the mold and 600F for preheating. Still playing with it. Cast 1000+ last night with a clean mold. It ran so smooth I didn't want to stop.

I would not buy the Sylvania Hot Plate again. It is not metal like I thought but plastic and is cracking. 1300 watts is plenty though.

[Enyaw]

Rapine bullet mould prep works fer me. Micro grafite in alcohol. Track of the Wolf sells it now that Rapine is gone. Keeps stuff from sticking in the first place. Too thin to change the mould specs. unless slobbered on way too much.

[DerekP Houston]

was just eyeballing my brass molds and found I have an issue on the new #68 clone from mihec. Will give this a try and see if I can get it cleaned out, might need to order some beeswax.

[Phlier]

I apologize if this has already been suggested, but solder removal braid/wick should work pretty well for this. Stuff like: https://www.amazon.com/gp/product/B01ESUKNXG/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1. Solder removal braid comes in all sorts of various qualities. Some work really well, some don't work worth a darn. I can't seem to find my supply of "good stuff" that i've had for years, so I just ordered the braid in the link to remove a few bits of alloy adhering to a few spots on a mold. I have no idea if the wick in the link is good or not. I guess I'll find out tomorrow when it shows up.

To use it...

Start by cleaning off the offending alloy so that it is completely clean and free of any oils.

You're going to want a pretty high wattage soldering iron for this. Place the end of the desoldering braid at the mid point of the alloy you want to remove. With firm pressure, press the tip of the soldering iron onto the wick, just barely behind the very end of the braid. Wait for a bit, and the desoldering braid will cleanly wick the alloy into it. It's important that you heat the wick up, and allow the wick itself to melt the alloy. I recommend a chisel point on the soldering iron, one that is the same width of the desoldering braid, so that you can evenly heat the braid along it's entire width. Repeat as necessary, but the braid has such a high propensity for lead/tin alloys, it'll usually come completely up the first time. The desoldering braid does have flux in it. Make sure you thoroughly remove the bit of oily residue it'll leave behind. You can get wick in various widths, so buy one that matches up for your use. The link posted above includes a solder sucker along with a spool of wick. The solder sucker is nice for sucking up larger areas of alloy. Sometimes the sucker will leave a bit of alloy behind, and that's easily cleaned up by following up with the wick.

If you don't have success with the wick you got, try others. You would think that there wouldn't be much variance between different brands of something as simple as desoldering wick, but there is. Some are also made to remove very specific alloys, so make sure that you get a wick that is made to remove lead/tin solder.

[Loudy13]

Glad I found this thread, I am having a problem with one spot on one of my brass molds and don't want to damage it.

Thank you

[Lead pot]

Once a brass mould gets tinned it's hard to get it cleaned. This is not much of a problem with a iron mould where you can put a wrap of fine steel wool on a bore brush or just a brass bore brush and close the mould on it and spin it. This will not hurt a iron mould but brass would be a different story.
I have brass moulds and I like them better then iron, little heavy but they cast a good bullet. When your alloy is tin/lead or tin/antimony/lead you have a solder and it does not mater with the amount of tin that is in the mix. Tin is the Villon that causes it. Chances are colcolt that all of your problem started with a clean mould from the start when you first used the mould. A pot full of alloy and fluxing the alloy and starting to cast with out having all of the flux burn off the alloy or some still on the ladle if you use one to stir the alloy with it. All a good combination for tinning the brass from the start and it just kept building up.
Opening the mould to soon before the alloy is set can pull some off at the parting line, especially if a fresh cut mould still has some burrs on the sharp edge. I use a paper towel and gently wipe the edge before I use the new mould. If there is a sticking problem this is where it starts.

[AllanD]

I have a brass mold I'm frankly scared to use because of the potential of alloy "soldering" itself to the cavities.

The mention of "patina" makes my mind immediately jump to Potassium Sulfate, to intentionally Blacken the surface and thus create an artificial "patina".

By the way, mixtures of Acetic Acid and Hydrogen Peroxide is basically making "Para-Acetic Acid" and it's action on Lead is to convert the lead
into "Lead Acetate" which is formerly known as "Sugar of Lead" as it is Sweet to the taste should you be foolish enough to taste it and is one of
the most "Bio-Available" lead compounds known as it is water soluble where most Lead compounds are not

[shootinfox2]

Try a plastic dental pick.

[kevin c]

I think I'm having the same problem with my MP and Accurate aluminum molds.

I hadn't seen anything until after a break in casting of a few months - dark, rough spots on the mold faces clustered at the edges of the cavities, that I didn't see when I put them away (maybe oxidation of the deposits?). Almost all the spots are between cavities at the sides, where the metal is thin (6 and 8 cavity molds), not at noses and not on the end cavities, where the mold is thicker (temperature difference?).

These are so far very difficult to remove. Softwood sticks work a little on the smallest spots, but do nothing for the larger. Beeswax on the heated molds did not change the spots at all, and I heated the mold hot enough to scorch the towel I put it on. I tried rubbing the spots with ingots of alloy while the mold was hot - pure just smeared and the harder alloys may have marred the mold face.

I have some scrap hardwood flooring that I'll try cutting into dowels for harder scrapers. I'll try a Kroil soak. I know citric acid solutions will take rust off of steel easily. I may try that on the marred mold.

Any other ideas?

[RedHawk357Mag]

I haven't had this issue with alum but I have with brass. For clingy lead boogers I keep a piece of burlap nearby to give a light scrub when mold is at operating temp. I would imagine the Kroil soak and wood tooth picks would probably be the safest course of action. With the brass molds I definitely have much better luck keeping lead boogers at bay with a good amount of heat cycling the molds before first use. While shiny brass molds are pretty to look at they tend to really gather lead deposits in my use. Definitely go slow and steady in your endeavor and probably not use anything harder than the aluminium.

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[quasi]

as I stated earlier in this thread, Bull Plate sprue lube and a chopstick cures all my mould problems.