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Dan Vanantwerp 07-20-2017 05:58 PM

Calcedony Prep
Got the glass cooking for a cobalt calcedony.
I've been looking back at the various post notes for working this temperamental glass.
One thing Pete has pointed out is a tendency to lose the colloidal swirls of color due to the normal rotation of the pipe post-gather. His recommendation is a "slap gather". While this is a colorful adjective, I'm not quite sure what it means.
I'd like to have a good strategy for working the glass so I can best evaluate the cooking ingredients and make adjustments accordingly.

So, how does one perform a "slapped gather"? :)

-or does it take two?


Jordan Kube 07-20-2017 07:42 PM

Don't worry too much about it. Anything you can do to manipulate the glass will make it fun. I like to drop some on the marver and then pick it up.

Dan Vanantwerp 07-20-2017 08:12 PM the Dino Rosen video I watched.

I saw the torso pic you posted. Very nice!

Pete VanderLaan 07-21-2017 09:02 AM

It's really helpful to not stir calcedonia glasses. If you do, they start to turn gray. So "slap gather" is just what it sounds like. Have an interior gather ready, as big as you want and then dip down on the side of that gather, lift up, rock it back and forth unless you like messes, and pull away from the pot. It will show the veining very clearly that way if it's a decent glass. I have seen people get directly above the pot and go straight down in and straight back up getting vertical veins. As Jordan suggests, you can lay out pieces of what ever shape you want on the marver and pick them up. Fred Warren was doing some beautiful work doing that.
I've long suspected that Dino as mercury in his calcedonia. I can't think of anything else that would make it so effective.

But don't stir it. It also likes to be thick.

Dan Vanantwerp 07-30-2017 09:57 PM

2 Attachment(s)
Thanks for all the help. I feel like I owe it to CW to follow up with my results.

My first attempt was a cobalt mix that failed to produce opal swirls. I am using crystallica and wanted to see if the cullet/squiggles would work without fritting the glass.

I changed things up and made a clear calcedony mix (no cobalt) based on Pete's recipe for calcedony and fritted glass. Huge difference!

I'm loving this glass. My furnace is a custom wire melter in which is housed both my 80 lb crucible and a 17 lb "color" crucible I got from Sundance. I built separate openings for both crucibles. I just dip into the calcedony, pull out the gather and cut the tail with a pair of turning!

As the glass cools the swirls appear...more heat/cool cycles=more color!

I haven't quite got the red to express very well yet. Any advice to expand the color spectrum would be very welcome.

Thanks again to those who have shared their experiences with this color and especially Mr. VanderLaan.

Jordan Kube 07-31-2017 05:06 PM

Add some copper and you'll really get to see those other colors expressed. Sometimes.

Pete VanderLaan 07-31-2017 05:30 PM

Don't add much.... think mercury if you like life is the fast lane, sulphide form

Shawn Watt 07-31-2017 06:36 PM

Ive got to ask .. how does the mercury act in the glass? I cant find any info on this.

Pete VanderLaan 07-31-2017 07:46 PM

It 's an area to go into. Dino Rosin was getting reactions I have not seen and it's the only area where i haven't gone. My translator at the time was not willing to translate the observation for me at the time and I thought that was significant. That was at least ten years back and i never pursued it. I still have the compound. I was at a loss as to show how Dino got to the exceptional reaction he got otherwise on the guitars.

Eric Trulson 07-31-2017 08:00 PM


Originally Posted by Pete VanderLaan (Post 135950)
Don't add much.... think mercury if you like life is the fast lane, sulphide form

Have any hunches as to whether you could use cinnabar in mineral form for this, or would you want to go with reagant-grade mercury sulphide?

I poked around a bit online, and the cheapest source I could find for 99% mercury sulphide was $80 for 50g at sigma aldritch. Easier on the wallet if you could get away with using crushed cinnabar instead. Or it might not be that big of a deal if the mercury is only getting added in very small quantities.

Mitcheal Veenstra 07-31-2017 09:28 PM

wow! That's looking great!

so on our short list to try in the color pot this fall once we are back from Chuck's class at corning.

Dan Vanantwerp 07-31-2017 09:46 PM

I was working with the color again today and it started to get a little muddy. Remembered what Pete posted once about hitting it with acetylene to "wake it up" and it seemed to help.

I'll try the copper addition and will get back to the cobalt as well.

I found that it could also be left on the surface and even did a stannous treatment that looked really nice.

Pete VanderLaan 08-01-2017 07:32 AM

I would certainly try the cinnibar. I'm not really familiar with it. Glass never needs more than technical grade and the only thing you have to watch out for in compounds is to note what's there in what quantity. I think the mercury would be in very minor amounts if it indeed did work.Everything's minor. I think the silver nitrate content in a proper reducing glass body is 9 grams in 21 pounds.

The calcedonia does work best in the presence of a small amount of red iron which is a nucleator. The chemistry of he goop is long strands of molecules that absorb and reflect with variation. The effect is best when the molecules are large and they do gradually get smaller so the effect decreases. It works best in a high potassium glass and none of the cullets have potassium to any degree. They want cheap glass and it's why I make my own. As noted, stirring it makes it worse as all the color effect mixes and turns gray. The heavy reduction from acetylene does help but there's nothing like a nice fresh pot. Eventually it will turn transparent amber. Doing the cobalt becomes a fine line between too much and too little. Copper in very minor amounts causes a red strike in the lehr.

Dan Vanantwerp 08-01-2017 10:42 AM

Hi Pete, To your (extensive) knowledge, do any of the commercially available batch mixes have a good potassium content for the purpose of calcedony?

I am slowly moving toward mixing up my own glass but in reality my space would not lend itself to a high volume chemistry area.

Pete VanderLaan 08-01-2017 11:45 AM

I wrote the best clear formula I've ever written for Spruce Pine last year. It's what I use but Spruce Pine has indicated that it does not want to produce the stuff because they have trouble storing Potassium compounds, SO Jim Myers at East Bay has indicated that he will produce it but it won't be pelletized. It's a custom batch at this point and not a stock item.
When John Croucher and Mark Peiser and I were bouncing these ideas off of each other, I submitted this one to John at near the end of two months work, he looked at it and said "I cannot find a single thing to object to in this glass". I wrote a second formula to marry to it which is unoxidized, which is important.

For me that's the highest praise I can get. I think the world of John and Mark. We had the best dinner at Tony R's with Eveline from Shanghai at Corning last June and simply closed the restaurant.

Dan Vanantwerp 08-02-2017 03:13 PM

I've contacted Jim and left a voicemail. When it's available, I'm hoping to get some of your potassium batch to optimize the calcedony effect. I'll test the compatibility with Crystallica as an encasement glass and see what happens.

Pete VanderLaan 08-02-2017 03:19 PM

He'll need the formula, but Jim and I always like talking to each other. Old War Horses.

Scott Novota 08-03-2017 12:42 PM


How would the formulas from the class marry to your new batch?

Pete VanderLaan 08-03-2017 01:53 PM

There are two different batches. The one I primarily tout as great is a Clear formula with a barium presence, little calcium and no borax but a lot of nitrate. I would not be inclined to use it as a calcedonia base but it could work, it will just take extra black tin and probably more silver to fight off the nitrate,

BUT... It is also designed to marry to the unoxidized formula which I provided the class years ago. If you were matching it to Cristalica ( which is how it's spelled) the Cristalica would be about a half point higher than mine which is tolerable. Mine just sits on SP87 as the target expansion.

It might be the case that either Spruce Pine or East Bay could mix that since it contains no nitrates at all eliminating the hydrophilic tendencies of potassium that Spruce Pine has problems with. Neither has the formula but I can provide it to them.

Dan Vanantwerp 08-03-2017 03:01 PM

Jim called and sounded interested in batching your formula. He wanted me to pass on my furnace specs. It's a wire melter and he is concerned about melting batch in it..specifically if it required higher temps. Funny, I was just reading the Antiques and Classics thread on this issue the other day. I do recall that you like to melt calcedony at a lower temp (2180, I believe) which my furnace can easily handle. Would this also be the case with the potassium glass?

Sounds very doable to me. I'll only be doing small batches in a 17lb crucible. The furnace is made to keep the majority of the crucible contents away from the elements. I can live with some loss of element life if the colors blow me away.

Pete VanderLaan 08-03-2017 03:25 PM

I will need to know what mesh sand Jim uses and it really needs to be a 200 mesh. Since he doesn't pelletize, it can work. You just have to charge in tiny amounts. There's nothing in it that would attack your elements. I need to talk to him anyways and always look forward to it. The number of people you've known fifty years at this can be counted on one hand usually.

What I don't know is how much a minimum for him to mix is. If you were doing the unoxidized, it would take a long time to use a ton.

Dan Vanantwerp 08-03-2017 03:55 PM

I made it clear to Jim that I would be experimenting to start with and that I am not a big production studio (I usually only buy 500 lbs of Cristalica at a time). He sounded OK with that.

Sorry for my spelling errors...I probably don't have calcedony right either (Chalcedony?).

I'll let you guys take it from here and look forward to trying it out.

Scott Novota 08-03-2017 05:42 PM


Please let me know when you have this locked in I would like to give it a run myself. I would not mind pulling smaller(500lbs) order to start off with to give a go.

Pete VanderLaan 08-03-2017 07:01 PM

It's been locked in for a year now.

Jim and I talk like we're both going to the beach and who cares.? We'll get there.

Scott Novota 08-07-2017 04:20 PM

1 Attachment(s)
Well I cooked some up over the weekend in the mini furnace. Figured I would add my tumbler to the mix. It really blows my mind that it comes out of the crucible clear.

Using it on the inside of Conch shells but they are all still in the hot box.

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