CraftWEB Hot Glass Talk

CraftWEB Hot Glass Talk (
-   General Hot Glass Discussion (
-   -   Dark Bottle Green Recipe (

Jacqueline Knight 09-16-2020 09:04 PM

Dark Bottle Green Recipe
3 Attachment(s)
Hi there! It's been an awfully long time since I was here, but thought I would ask a question. I hope everyone is doing well!

Does anyone have any recommendations for a dark bottle green recipe? We melt Gaffer Batch here at the Canberra Glassworks. I have a recipe for a tealy-green but it is not dark enough.

Per batch of 100kg it is:

Iron 500g
Cobalt 1g
Nic 1g
Copper 20g

I saw this thread from 2014:

I have attached an image of the density we're after as inspiration. I have also attached some pics of samples of teal greens that we already melt, they're too light. Any suggestions? How about this one below?

Olive Green Bottle Glass
sand 100 kilos
potassium chromate 500 grams
manganese dioxide 1500 grams

If anyone has any recommendations that would be wonderful.
Thank you!

Josh Bernbaum 09-17-2020 09:26 AM

I'd first remove the copper. I don't think that's helping you any.
I have only done light/bright greens with chrome, with iron, and with vanadium. The base batch you're adding to will vary what effects you can expect from the colourants in most cases.
What I would think about trying if doing this myself would be chrome or iron with a bit of nickel maybe? And it'd be a trial-and-error, no way around it, to get to the concentrations that look the best. I like to do small test melts if I have time, which quickly give you a decent sense of the final colour after the batch goes flat in the furnace, although things do darken up a bit in my experience after the full melt/fining process. If you melt 2-5 kilos at a time, then it's easy to multiply for a larger melt later. The chrome and manganese may start getting a bit too brown/ugly-violet for you, because the chrome will 'activate' the manganese and make it have a stronger effect. But perhaps a little bit of manganese with the chrome will steer you towards a darker shade versus the nickel I mentioned. I think whether Gaffer's batch has any potassium in there, or just sodium, might come into play regarding that. Be careful with the chrome, but grind it up in a coffee grinder (Pete's trick) if it's the dichromate form, to get it into a fine powder vs. lumps. And don't skimp on the melt temp to help it go into solution and not form corundum flecks. It may also be the case that all you need is a boatload of chrome to get it to darken up the usually bright green shade it produces in a soda/lime batch. But the more of any of these colourants you add (some more than others of course), the more likely you're throwing off fit with your clear. But if you're not gathering over the colour or mixing it with clear or other colours in any way then have fun and experiment with increased concentrations of these colourants.

Pete VanderLaan 09-17-2020 11:57 AM

I'd be looking for some iron chromite and avoiding the hexavalent chromium scenario. Avoid reduction. I'll see what I can come up with in the formula library I have. It's not a color I ever make for myself. Copper and iron do make some lovely greens but only in a lead base.

Jacqueline Knight 09-17-2020 10:38 PM

Thank you Josh and Pete! I appreciate your input. We have been discussing melting half a bag of batch (10kgs) to test and see through a bit of trial and error. We have an 80kg colour pot furnace and want to melt some tests in the same atmosphere.

Interesting you ask about Gaffer batch re potassium or sodium. I can probably look up the MSDS. I like the idea of Manganese. Also just upping the Pot. Dichromate. We will just be blowing it straight and not trying to fit it with any other glass or colours so at least that is something we don't need to worry about.

Thank you for the note about the coffee grinder! And I look forward to any further information you can add, many thanks Pete :)

Pete VanderLaan 09-18-2020 06:12 AM

I am encouraging you to try to get away from the dichromate. It does produce hexavalent chromium which is well established as a carcinogen. Iron chromite would help with making the bottle green without those same issues. The great difficulty with chrome is its refractory nature and inability to be taken into solution. I have not been out to the studio to pursue recipes in the library but John Croucher and I were discussing this very issue a few months ago.
It would help to place any chromium compound you use in some lithium carbonate prior to the overall mix giving it a nice bath in some pretty aggressive stuff. I do that when making my dense black. These days, I use a juicer I got at a flea market. I got lots of them actually. They never last all that long.

I don't see why manganese would be helpful at all.

Peter Bowles 09-20-2020 04:46 AM

Hi Jacqueline, it looks like an Iron Chromate and Iron Oxide blend to me. I've got some samples from way back somewhere in the studio, I'll have a look in the next couple of days.
If you are serious about getting close to the tone and saturation there is a very useful system to use by casting a wedge shaped piece of glass from every sample you make. Firstly, it gives you a calculable colour density at any given thickness. And secondly (and even more usefully) it allows very quick tonal variations to be seen with variable thicknesses of two or more glasses.
Curious to know how much you will need to melt for your project?

Jacqueline Knight 10-11-2020 11:25 PM

Hi Pete and Peter,

sorry for the delay in responding! Thank you so much for your replies and additional information. I would definitely heed your advice regarding the dichromate vs Iron Chromate. It is wonderful to get your opinions on this.
We do have a wedge mould for colour tests that we use. Initially we will melt small test batches, possibly 10 or 20kg melts to make sure we have the mix right, then we would melt an 80kg pot furnace. Our 400kg tank furnace is only used for clear.

Pete VanderLaan 10-12-2020 09:22 AM

Iron Chromate= Fe2(Cr04)3
Iron Chromite = Fe2(Cr04)

All times are GMT -5. The time now is 01:22 AM.

Powered by vBulletin® Version 3.7.2
Copyright ©2000 - 2021, Jelsoft Enterprises Ltd. Opportunity Network. 2008. All Rights Reserved.