Does anyone have experience or understand the principles of using crushed glass as flux?

I was browsing the forum when I came across an old post about using crushed brown beer bottles as flux for copper and bronze casting.

This is the second or third time I have heard of using crushed bottles for flux.

They both emphasized how important the color of the bottles were

I understand the basic principle of using glass as flux. It melts at a lower temp than your metal and creates a physical barrier keeping oxygen off of your metal.

They said two completely different color of bottles to use. 

One guy said "he uses brown beer bottles and that the iron in the glass  helped to remove impurities when casting bronze and copper."

The other was a goldsmith who said that once you have overworked gold you have to melt it with green glass bottles to "fix the metal".

I know that glass has different melting temperatures, but is that the only reason? Or  does it come down to different color glass has different elements in them for different purposes?

 

 

IIRC Thomas Powers had a lot of experience and a lot to say on the subject but it was beyond me. 

When I hear a smith other than black, use "fix" in relation to the metal I read it as "stabilize" rather than repair. I don't know what pigment is used to color glass green but three are a lot possible. The ones I know of that have an affinity to gold being, copper, arsenic, zinc. I don't know if Paris or Sheele's green can be used to color glass but both are asenic containing pigments.

Three are other green pigments but I don't see why Chromium oxide would be beneficial for fluxing gold. 

Then again the impression I always had about covering a cupric alloy with crushed glass or white sand was to produce a prophylactic layer to keep the oxygen out and you'd stir in charcoal to deoxidize the melt just before you pour. 

Sorry for the long reply that pretty much comes to. I don't know.

I sure miss Thomas and his material sciences doctorate at times like this. Might be able to find something he said in a search.

Absent companions.

Frosty The Lucky.

I appreciate the response Frosty. 

Your "I don't know" has a few threads probably worth pulling.

If i was a smarter man you may have answered my question and i just don't  understand it.

I wish I could have talked to Thomas as well. I have read many an old post/responses from him. He was definitely the final word. 

 

I once used fine silica sand as a flux (basically the same as crushed glass) and it worked OK but was sticky and didn't melt as readily as borax.  I have always thought that a mixed silica/borax flux might have virtues but I have never tried it.

G

I’ve forged some glass-lined water heater steel, and the glass is viscous enough that I’d worry about it getting trapped in a weld. And come to think of it, that’s exactly what does happen with wrought iron. 

George and Mike, remember that we’re talking about casting, not forge welding. 

George is right about using sand. Just not sand alone. (Also about mixing sand and borax.)

Quick story time. For many years the US mint was the only mint in the world that could produce .999 fineness gold. Other countries could only make .900 fineness.

Why? Because they couldn't get rid of that last tiny portion of silver.

It all came down to the flux. Manganese dioxide was the secret ingredient.

Since I'm giving out secrets. Does any one want the original mint flux recipe for gold?

*Three parts Borax glass

*One part Sodium Carbonate

*One part Silica

*One part Manganese Dioxide

 

 

To how many parts gold?

Frosty The Lucky.

Since I'm talking about flux I'm going  to try and get ahead of this.

Im not here to argue the semantics of Smelting, Melting, and refining.

I have seen this argument many times before. This is my definition.

You use diffrent fluxes to pull out different impurities from the gold that will run out with your slag.

It can be ore or an alloy.

Impurities is only a word relevant to what you are trying to accomplish at a given time or task.

If your starting material contains a large amount of silver you would not want to add manganese dioxide.

You would be losing all the silver in the melt. You would want to recover the silver first.

If you melt gold, add flux,and pour a bar that is purer than it started that is refining by definition.

Frosty,

Two parts flux to one part material being smelted.

 

 

 

I wasn't trying to be a PITA I only wondered if there was a rule of thumb about how much flux to add to a given weight being melted. If there are too many variables for a simple answer that's a good answer.

Frosty The Lucky.

Frosty, 

For instance if i was stating with placer gold it would be one part flux to 3 to 5 parts gold.

My flux wold be in a diffrent ratio and I would add lime-Flourspar mixture.

 

*starting

Your fine Frosty. Too many variables.

Edit*

Placer Gold

3 to 5 parts flux to one part material

 

I think I might have figured it out.

I just got home from home depot. My girlfriend only drinks the mexican cokes in glass bottles.

What color would you call that glass? You guessed it. It has a hue of green to it. Not clear. However they do come in completely clear and green. She said the clear ones were all flat last time she got them.

I was thinking Heineken bottles in my mind not coke bottles.

Apparently both green and brown (amber) bottles contain iron for color and a few minor additives like aluminium oxide, magnesium oxide, and sulfur.

 

So basically the crushed glass is being used in lou of mixing your own flux and with the addition of iron to pull out impurities.

Long story short the glass is pre-made flux. And you want one with iron in it.

When I was a kid, "Coke bottle green," was a color, pale transparent, like a not too old insulator. I lived too close to Tijuana to be tempted to drink Mexican sodas. Beer, Oh yeah but not the soda and certainly not the water. 

Florida today is a way different place than S. Cal when I was young enough to go to Tijuana for the . . . relaxed age of adulthood thing. 

Frosty The Lucky.