Casting two metals, cold and hot.

[Chinobi]

so I was curious about the extent and severity of the brass/silver eutectic reaction and looked around on google for a bit and found this.  the second paragraph of the long response has an explanation of the process as it relates to heating solid parts of both metals in contact with each other, though I would imagine the same would happen if one or the other started out molten.  iv ordered some sterling casting shot as I am low on scrap at the moment and have a couple of fun, hopefully educational, test projects in mind to explore the severity of the reaction for future projects.

 

http://newsgroups.derkeiler.com/Archive/Rec/rec.crafts.jewelry/2007-04/msg00068.html

 

im not 100% on if its ok to direct quote it, but it mitigates the potential for the loss of said information, excerpt from a thread regarding granulation in jewelry:

"This is similar to what happens if you place a piece of brass, with flux, on a
piece of silver and heat them. Because brass alloyed with silver forms a lower
melting alloy (silver solder, to be exact, any of several grades depending on
proportions), at the melting temperature of the lowest melting of the
combinations of silver with brass (the eutectic temp of that system), the two
still solid and unmelted surfaces, of brass and silver, will combine without
first melting. They do that because the contact area itself, rather than one
surface or the other, allows that eutectic alloy to form, melting the interface.
This proceeds, of course, dissolving more and more of both surfaces into the
mix, forming more of the eutectic mix. With silver and brass, the potential
drop in melting point, ie the difference in temp between the melting point of
the eutectic mix and that of the two parent metals is rather large, leading to a
rather rapid combination when an unsuspecting jeweler heats the two together,
perhaps trying to solder them together. The brass can quickly sink right into
the silver as it does this, combining the two sometimes disastrously. I
suspect, but don't have data in front of me, that the reduction in melting point
that occurs at the contact between gold and silver is slight, making it a
controllable situation."