"Crying" Tin

[Alchemist]

I've had "pure" tin bars in the past, and of course they would crackle when bent. I recently melted down some estate sale pewter and made my own bars in a mould for making decoy anchors. The resulting bars crackle like tin when bent, but seem harder to bend. Since pewter isn't pure tin, how low can the percentage drop before it won't cry anymore?

Am I overthinking this...should I just consider my pewter to be 80-85% tin and go with it?

Chime in with your experiences. (especially you metallurgists)

[I'll Make Mine]

What I recall from college "material science" is that the noise when bending pure tin is due to crystals "twinning" -- a sort of same-phase phase change caused by large-scale crystal dislocations that propagates through the material faster than the speed of sound in tin, so producing a "click" -- get a lot of clicks close together, and the tin "cries."

This should happen with any tin alloy that enjoys the same crystal habit and shows the same twinning behavior; that would probably require the alloying metal to have a similar atomic radius to tin, so as not to pin the dislocations (dislocation pinning is how carbon, in controlled quantity, hardens iron to form steel). As a best guess, there should be a family of tin/lead/germanium or tin/bismuth/gallium alloys (maybe a tin/thallium/arsenic family, too, but I wouldn't want to handle the stuff) that preserve the "click" crystal twinning at varying levels of hardness, varying melting/annealing points, etc.

[Alchemist]

Good info...thanks. I've googled and searched and couldn't find an explanation of where the cry comes from.

[runfiverun]

i have some old body lead that has 30% tin and i can just barely hear the creak of the tin in them.
could be my hearing though.
but yeah it's more a cracking sound than a creaking to me.

[lwknight]

Just consider it pure tin and go with it.
Its probably more than 90% anyway.

[imashooter2]

I'm with lwknight on this. When I add modern pewter to my alloys, I consider it 100% tin.

[Old Ranger]

I've been a pewter hunter for the last six months or so. I only buy objects which are marked pewter. Most common find is beer tankards and wine goblets. My understanding is that modern pewter used for drinking/eating utensils is lead free (makes sense). My last find was 8 goblets marked Belgian pewter and 94% which I assume is the tin content. Odd thing is that while all these objects have a very high tin content -they melt at a low temperature and are easily bent/cut- not all make the "crying" sound when bent. Is this because of what the remaining metals in the alloy are? I use as pure tin when adding to my WW.

[I'll Make Mine]

Odd thing is that while all these objects have a very high tin content -they melt at a low temperature and are easily bent/cut- not all make the "crying" sound when bent. Is this because of what the remaining metals in the alloy are? I use as pure tin when adding to my WW.

Exactly. Bronze, for instance, even if made with tin content above 80%, won't cry; the copper atoms are enough different size from the tin to prevent the rapid dislocation movement that makes the noise. Modern pewter typically contains 1% to 2% tin, as well as antimony up to 5%; I'm not certain of the effect of antimony (the atomic radius of antimony is very close to that of tin), but 1% copper is likely just as effective at locking dislocations in tin as 1% carbon is in steel.

As long as the stuff was made in the past fifty years or so, it's likely perfectly fine to treat it as pure tin for alloying (given no more tin than you'd usually add, the antimony will have very little effect and the copper none) -- it's very unlikely to be any less than 96%. I wouldn't worry about it not making noise when you bend it.

[runfiverun]

copper and tin have a tendancy to slide over each other rather than lock up and pull apart.
tin will do the same thing in other metals also it will break apart and rebond with them but it acts like little bearing areas within the alloy.
it acts much differently in ferrous and non ferrous metals.