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-   -   Chalcedony, Silver Opal (http://talk.craftweb.com/showthread.php?t=12464)

Ed Pennebaker 11-08-2019 09:12 AM

Chalcedony, Silver Opal
 
1 Attachment(s)
I melted a new color this week. It looks pretty good but I would like a little more red tone to it. It is a dark amber in transmitted light. Recipe for 100 pounds Spruce Pine Color Base
300 gm zinc oxide
280 gm black tin
46 gm silver nitrate
20 gm red iron oxide
melted at 2125, taken up to 2260 7 hours after last charge.
Fairly seedy first day, fewer very small seeds second day.

Should I use a little less red iron or less silver nitrate?

Chris Lowry 11-08-2019 11:51 AM

I really know nothing but the old guys talked about adding sugar to help reduction.

Pete VanderLaan 11-08-2019 12:46 PM

Chalcedonias really like potash and really don't like sodium. zinc and black tin are OK silver seems high, iron somwhat low, melt a lot hotter. Neutral flame. Don't add sugar. That glass will be a slight mismatch for SP87

Read the first sentence again.

Ed Pennebaker 11-08-2019 01:48 PM

"Chalcedonias really like potash and really don't like sodium". So I assume that means I would need some potash to help it go toward the red instead of browning out.

Pete VanderLaan 11-08-2019 02:55 PM

several things can cause the browning. The first I would indeed say is the sodium content which you can't reduce since it's pre mixed. Second would be the excess silver and it's very touchy as to when is too little and too much. In my own formulations, two grams either way makes for a major shift. The batch doesn't need more zinc since the base has lots. Iron can be strange, Too little and it just strikes poorly, Too much and the same thing happens but the non strike is very different.

Also heating and cooling those glasses is really important for the strike. If it is turning amber prior to any reheat, it has probably got too much silver. I can't quite put a finger on it because of the sodium which I avoid so I don't really get to see its influence.
Reds come from adding a remarkably small amount of copper. They strike in the annealer.

Greg Vriethoff 11-08-2019 05:33 PM

Neato!

(Seriously. I love this stuff.)

Larry Cazes 11-09-2019 07:46 PM

Quote:

Originally Posted by Ed Pennebaker (Post 145825)
I melted a new color this week. It looks pretty good but I would like a little more red tone to it. It is a dark amber in transmitted light. Recipe for 100 pounds Spruce Pine Color Base
300 gm zinc oxide
280 gm black tin
46 gm silver nitrate
20 gm red iron oxide
melted at 2125, taken up to 2260 7 hours after last charge.
Fairly seedy first day, fewer very small seeds second day.

Should I use a little less red iron or less silver nitrate?

Thats really nice!

Ed Pennebaker 11-26-2019 08:44 AM

second batch
 
1 Attachment(s)
The second batch does have better color I think, the photo make it look a little more red than it actually is. But it has some deep maroon, purple and blue. Decreased silver by 2 grams, added 60 gm black copper, melted hotter. It does strike some color in the annealer. The best color pieces are put in early in the day at the back of the annealer. I had to make a batch of cobalt between the two batches of Chalcedony so there was some extra cobalt also. Early checks on melt progress without reheating the glass looked like a light cobalt I usually make with 3 grams of cobalt in 100 lb of SP87 plain batch. It is still very dark amber in transmitted light.

Pete VanderLaan 11-26-2019 09:05 AM

That looks great Ed! I think you can back off of the copper even more. Those glasses don't take kindly to being gathered. It tends to mix the colors up. Slapping it on the side of a piece is more effective, or taking rope like gathers that are slapped and then drawing them out and annealing them to be picked up later on the sides.

When I wrote the formulas for the Corona glass Josh Simpson was making, I told him he could only do three, perhaps four pieces a day unless he was willing to set up a second pot for the color. The surface of the pot is affected by local reduction but as you get into the melt, that slows way down and the stuff tends to turn either gray or eggnog color. You can draw it up if you chuck tiny balls of wax into the pot and gather quickly. Simpson used a rather large oxy acetylene torch on the pot surface. It all works.

Ed Pennebaker 11-26-2019 01:15 PM

Since I only have one furnace, one pot I take a gather or two, pinch, cut, and mess with it getting the gather very uneven until rather cool. Then reheat to develop the color. I have to reheat and block it several times to get it even again. Timing is difficult to get down, no two pieces the same but I like what it is doing.

Pete VanderLaan 11-26-2019 02:55 PM

well, it looks nice. I'm glad to see the reduction in the quantity of silver worked out. Do stay away from the sugar and it already has lots of Zinc from the SP87.

Eben Horton 11-26-2019 05:42 PM

Beautiful stuff Ed !!

Scott Dunahee 12-02-2019 12:53 PM

just for giggles, before you pinch and abuse up the gather, roll it in some other silver bearing color frit. Trust me. Or at least try it....

BSD

p.s. those look great, Ed.

Pete VanderLaan 12-02-2019 03:27 PM

tiny copper wires... think tiny copper wires, really small.


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