making cabochon with coin inclusion?

[BadExampleMan]

I had this idea to make some cabochon beads with coins inside them - a sandwich of, say, black on the bottom, clear on the top, with a penny in the middle.

But everything I can find about the composition of common coins and the melting points of their alloys says this probably won't work - the melting points are too low so I'd probably end up at best with an unidentifiable blob of metal. And of course the COEs are all wrong.

I still want to try it, if for no other reason to see if the failure looks interesting - but would anyone advise me O MY GOD DON'T DO IT YOUR KILN WILL EXPLODE AND SHOWER YOU WITH FLAMING METAL or is it safe? And are there any common coins with high enough melting points to stand full fuse temp?

[Marty]

It's "safe" but the glass will crack.

[GuyKass]

Almost all the precious metals melt at a higher point than you would be working at.

*Gold 1950F
*Silver 1761F
*Silver coins 1615F
*Copper 1981F

*http://www.kitco.com/jewelry/meltingpoints.html

You could probably easily accomplish what you want to do by doing it cold. 3 layers (hole for the coin in the meat of the glass sandwich), put the whole thing together with Hxtal, and the coldwork the edges.

As for just wanting to try it. Why not? That's how you learn.

[Judd]

Dude, American coins have a lot of zinc in them. I assume all countries use zinc because it's cheap - or they use the cheapest metal they can find. If you fire the coins, be sure your kiln is well ventilated, and don't hang around it when it's at top temp. Zinc fumes are quite deadly.

[BadExampleMan]

Thanks for the zinc warning - the coin I was going to try first is mostly zinc. That could've been unfortunate.

Looks like a US dime or an Israeli 1 shekel might be a good choice, they're both copper/nickel with a nice high melting point.

[Brad Walker]

Ok, here's what will happen:

Penny -- 97.5% zinc -- will be ok to fire as an inclusion. ZInc fumes are poisonous but there probably aren't enough from a penny to cause a problem. It's not the most beautiful look after it's fired, but some people find it interesting.

Dime or quarter -- mostly copper. The piece will crack after firing as an inclusion.

Nickel -- 75% copper, 25% nickel. The piece will crack after firing as an inclusion.

It costs 2 cents to make a penny, 11 cents to make a nickel, but both the dime and the quarter cost less to make than their face value.

And now that I've answered your question, here's one for you: If you won a contest and were given your weight in your choice of pennies, nickels, dimes, quarters, half dollars or dollar coins, which would you want? (U.S coins, no Googling allowed!)

[GuyKass]

Complete guess.

Dimes.

And considering what I weigh, I'd be rich!

[Kevin Midgley]

Gold dollar and half dollar coins!

[Brad Walker]

Gold dollar and half dollar coins!

Nice try. The US stopped making gold dollar coins in 1889. According to my father's coin books, the gold in them is worth around $70 today (not as much as I thought it would be).

A really good out-of-the-box guess would be the double eagle coin, which was a $20 coin that was made until 1933. The gold in them is worth around $1400 today. My weight in those coins would be somewhere over $5 million, enough to make me think twice about going on a diet.

[Eric Baker]

Thanks Brad!

I'll never look at a Sacagawea coin the same way (weigh?) again.

[Brad Walker]

I'll never look at a Sacagawea coin the same way (weigh?) again.

The Sacagawea coin is copper and brass. No gold. Unfortunately, the glass would crack if you fired it as an inclusion.

[BadExampleMan]

Well, the dime melted. And went through some kind of chemical reaction; it's now a featureless dull-copper-colored disk. The 1-shekel coin came through fine but it's surrounded by a ring of tiny bubbles and micro-cracks in the top glass. Kind of a neat effect, really.

I think I'll try again with some other coins, and maybe dropping the process temp a bit. I used 1515 and maybe that as higher than necessary.

[Tracy Fries]

I'll fess up...........tried it with pennies shortly after I got my first kiln about a year ago......ICK! They were more recent pennies - so high zinc content - and the reaction was sort of like a bubbling fizzy mess - not at all salvageable with any sort of coldworking. The resulting 'fizzyish' material was bubbly and gray and craterish on the surface of the glass.

[Peter Angel]

The piece will crack after firing as an inclusion.

Brad, what if you used very thick glass? Will it still crack?

[Brad Walker]

The issue is coefficient of expansion. The COEs of most metals are very different from the COEs of the glass we use. So unless the metal is really thin or if it's melting temperature is below fusing temps, the COE difference will cause the crack. A thicker glass may change the picture slightly, but not enough to overcome the COE difference. It's the thickness of the metal that matters most, not the thickness of the glass.

For those who are interested, here's some basic info on the COEs and melting points of various metals: http://www.warmglass.com/COESummary.htm#metal

[BadExampleMan]

Update: fail, fail, fail and fail. And FAIL. Not even salvageable as an interesting failure.

Trying a new approach...

[Lynn Perry]

Have you thought about pressing the coin into a thin sheet of copper and then firing the copper?

[Brock]

"And now that I've answered your question, here's one for you: If you won a contest and were given your weight in your choice of pennies, nickels, dimes, quarters, half dollars or dollar coins, which would you want? (U.S coins, no Googling allowed!)"

So . . . what is the answer?

[Brad Walker]

"And now that I've answered your question, here's one for you: If you won a contest and were given your weight in your choice of pennies, nickels, dimes, quarters, half dollars or dollar coins, which would you want? (U.S coins, no Googling allowed!)"

So . . . what is the answer?

http://datagenetics.com/blog/december42012/index.html

(This is a great blog to follow, by the way.)

[Ed Cantarella]

I've tried all US coins, old and new. Fizzy blobs of nothing. May have gone stupidly high - it was years ago and I have no interest in it now. Many coins might work if they didn't have the zinc(melts at 787f.) and tin(449f.) in them - plus alloys frequently have lower melting points than any of the metals in them. E.g. silver-bearing solder: lead melts at 621f, silver at 1763f. 2% silver with lead - melts at 430f. Silver bearing is nice - easier to work with due to lower heat and joints are nice and shiny. I do digital watch repair and it is all I use on those ancient circuit boards.

I think making a pocket in a sheet of glass for the coin to be dropped into with a crystal clear casting material around it would end up more satisfying. Glue is not cheating - at least not imo.