Heat cycle new mold open or closed?

[MAGA]

Hello, I plan on heat cycling a couple of my first molds tomorrow one is brass and the others are aluminum. I used the search feature and read through a lot of threads with no real consensus on this issue. Will there be an issue cycling the halves open to ensure patina will start to form in the correct places? Or should they always be heat cycled closed? I have a hot plate and a toaster oven
Thanks!

[MT Gianni]

I use NOE's recommendation of three cycles of heat up in a 350 oven then cool down to room temps. I see that once it gets hot then cools open or closed should not matter. I go with the two halves apart but pre-heat with them closed.

[mold maker]

Heat cycling is really just heat accelerated oxidation of the surface regardless of the material. It also relieves stresses in the mold, or at least that's what I've read. I have always followed the conventional wisdom and heated new molds as recommended, but the last brass mold I only had time to heat once. It preformed exactly as the rest, and as soon as it was up to casting temp it produced great boolits. It's entirely possible that this mold had less/no residual oils and had shelf life to produce the patina suggested for good production, but I was pleasantly surprised with it's quality of casts without the time required for a full cycle of heating/cooling.

[KVO]

The mold halves will heat up a bit faster with the blocks apart, but so long as they aren't air tight when heated they'll oxidize evenly on the faces. For me, preventing tinning at the lube groove corners of brass molds is the main objective, as they drop the same quality of boolits either way. Tinning is a pain in the butt to remove!

[dragon813gt]

The mold halves will heat up a bit faster with the blocks apart, but so long as they aren't air tight when heated they'll oxidize evenly on the faces. For me, preventing tinning at the lube groove corners of brass molds is the main objective, as they drop the same quality of boolits either way. Tinning is a pain in the butt to remove!

Pretty much what I was going to type. If you use an alloy w/ little tin, then tinning isn't an issue. But if you use one that does have tin it's a complete PITA to remove if it sticks to the blocks. I leave mold halves apart when heat cycling them.

[MAGA]

I cycled them apart 3 times so far gonna do one more
Thanks!