Yeah, I saw a picture of one of those sort of molds (first one shown) I believe I saw it called a tree of life?

I wonder what kind of wood the molds are made out of?  I would have thought that they would have charred into unuseability after just a couple of castings, the tree ones look uncharred.

https://fundamittere.jimdo.com/formenbau/

Wir haben das in Hedeby schon einige mal probiert. Es funktioniert sehr gut. Wir verwendeten Eiche als Holz . Besser funktioniert noch Buche. Wenn man die Form vor dem gießen mit Talkum oder Graphit auspudert , hält die Form sehr lange.

Not catching fire, charring.  If you look at the single molds, one of them showed signs of charring.  Pretty sure that one is some type of red oak. 

The interior won't catch fire due to lack of oxygen but the heat will cause the carbon in the cells of the wood to break down.

I cast bullets quite a bit, if you attempt to pour at just over melting temps of the various alloys, the lead will solidify while it is still flowing into the various voids.  Especially as the mold is much cooler than the metal.  In metal and ceramic molds, the mold will heat up in each successive pour and the lead will not cool as fast, thus filling out the cavities.  Pretty sure that while wood will get hot, it won't get hot enough to keep lead molten for the few milliseconds it takes to fill out the mold, so that has to be a rather dense wood without defined grain structure.  And the lead was probably well over twice the melting temperature, the glandes show signs of flashing and don't have the ripple look due to lead starting to solidify during the pour. 

Although the hollow spots shown are due to a cooler mold causing the lead in contact with the interior surfaces to cool and plug up the channel, and the void inside wasn't filled in.

BTW, they melted the lead on a stove, I hope for their sake's that the place had some type of forced ventilation, otherwise, they were breathing lead fumes.

Wir haben einiges an Erfahrung.  Bei unseren Treffen versuchen wir die verschiedensten Methoden . Holz funktioniert sehr gut wenn man es richtig macht. Wir haben professionelle Zinn und auch Bronze Gießer .
Im letzten Jahr wurde eine historische Glocke gegossen. Da sind unsere kleinen Glandes Peanuts .

Lead starts turning to gas at just a few degrees above melting temps.  Breathing lead fumes is not a good thing.  Hotter the metal, the more gasses it gives off.  I do my casting in a shed that has one side open and there is a large gap at the top and bottom of the sides.  This lets air flow easily.  I still avoid getting my head over the pot or mold as I pour.  And I sit cross ways to the flow of air.  If you sit in line with the flow, swirls can bring the fumes back to you.

If you cast out in the open, your exposure to lead fumes drops dramatically.  The heat from the fire sucks the fumes straight up and disperses them.  Still, keep your face away from the pot of lead and the mold as you pour.  And if the wind shifts and smoke starts getting in your face, move.