CraftWEB Hot Glass Talk  

Go Back   CraftWEB Hot Glass Talk > Hot Glass > General Hot Glass Discussion

Reply
 
Thread Tools Display Modes
  #1  
Old 07-10-2018, 05:02 PM
Jeff Wright's Avatar
Jeff Wright Jeff Wright is offline
Registered User
 
Join Date: Apr 2002
Location: Milan, Michigan, USA
Posts: 222
Jeff Wright is on a distinguished road
Melting batch in small quantities

I know most of you melt in large batches, but I have some questions about melting small quantities. I'm thinking about 500g of glass. First some background.

I've been glassblowing for about 20 years. I took Pete's second color class back in 2002. I have a lot of chemistry background so I understand a lot of the discussion. However, I have a chronic hereditary illness that requires a liver transplant eventually. Some of the side effects are confusion, lack of coordination, and loss of strength. I had to go on long term disability and SSD. I gave up my hobbies of glassblowing and woodworking so I wouldn't hurt others or myself.


I got a 3D printer and am making molds for casting. I need to keep costs down and make colors that I can't buy. I worked with an instructor to mix oxides into batch, melt in small crucibles, cool, and ultimately melt into molds. These tests were about 150g of batch. The crucible was a hand-thrown ceramic dish. The results were quite good. Note that I don't care about COE in this case.

So the questions: If I want 500g of formed glass, I should start with about 600g of batch, based on an earlier question. How much space should I leave in the crucible to prevent melting over? What is a good source of crucibles? I found DFC Ceramics in the archives. The sizing is quite confusing. Any idea on size for this project? What composition of crucible should I use, fire clay, fused silica, ...? I tested melting at 2260F.

Finally what do you think about reusing the pots? I know there is some color left in the pot. How much impact will this have on the next melt? I will weigh before and after to get a better idea of quantity of the residual. My guess is about 5%.


Thanks in advance.
Reply With Quote
  #2  
Old 07-10-2018, 08:38 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,278
Pete VanderLaan is on a distinguished road
In melts I do, a one half gram difference in the mix of 20 lb batches makes a significant color difference in the result. 1/2 gram. Not a lot.

You need some really good scales. Better than the ones I own and mine are really good.
Your cost on a 20 lb mix? Maybe 20 bucks. Make bigger mixes.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #3  
Old 07-11-2018, 08:06 AM
Dave Bross Dave Bross is offline
Registered User
 
Join Date: Apr 2002
Location: Archer FL(near Gainesville)
Posts: 2,943
Dave Bross is on a distinguished road
I've been OK mixing 10 pound total batches but below that not so much. I may not melt it all at once.

Assay pots are reusable if you don't mind them shedding a bit of iron into the glass. When assaying they pull them out of the furnace screaming hot, dump them and then re-shelve them.
Use the search here to find suppliers. Legend Reno Mine Supply is one and there's another one in MA that sells cases only. Legend is more expensive but will repack them for you so they don't break in shipping, which is a major problem.

Not to worry on leaving space in the crucible. You'll have less glass by volume than you did batch.

Here's a more expensive supplier of assay crucibles who give you the glass weights and volume:

http://www.sundanceglass.com/cruciblesr.php
__________________
Art is not a thing...it's a way.
Reply With Quote
  #4  
Old 07-11-2018, 08:44 AM
Steven O'Day Steven O'Day is offline
Registered User
 
Join Date: Jun 2002
Location: portland oregon
Posts: 296
Steven O'Day is on a distinguished road
This has me thinking about glass formulas for casting. Anyone have some ideas they would like to share? It seems that ignoring compatibility and concentrating on low devit and flowing properties in the mold could open up some interesting possibilities.
Reply With Quote
  #5  
Old 07-11-2018, 08:50 AM
Steven O'Day Steven O'Day is offline
Registered User
 
Join Date: Jun 2002
Location: portland oregon
Posts: 296
Steven O'Day is on a distinguished road
I mix 100g glaze test batches. Our scale reads to .01 and we try to get it to that precision. Ceramic glazes aren't as critical as glass but it works.
Reply With Quote
  #6  
Old 07-12-2018, 09:06 AM
Ted Trower's Avatar
Ted Trower Ted Trower is offline
Registered User
 
Join Date: Apr 2002
Location: Ann Arbor, Michigan
Posts: 518
Ted Trower is on a distinguished road
Jeff - sent you a craftweb pm.
__________________
"It appears to me that glass men are the most given to drunkeness of any class of men I know" Peter Burt, recruiter in Europe, in a letter to Deming Jarves of the Boston and Sandwich glass company. -1826
Reply With Quote
  #7  
Old 07-12-2018, 12:56 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,278
Pete VanderLaan is on a distinguished road
Quote:
Originally Posted by Steven O'Day View Post
I mix 100g glaze test batches. Our scale reads to .01 and we try to get it to that precision. Ceramic glazes aren't as critical as glass but it works.
********
I balk at small tests in concern for materials taking on water from the air. It strikes me that the potential for error goes way up the smaller the sample size and at a certain point begins to question the law of significant figures. In Ceramic glazes , it's not the same issue since you are not really dealing in mismatch.
That in turn ties into the way the melt is done. The surface area of the pot has a lot to do with how color presents. Glasses in general are only affected
by the kiln atmosphere down about 1/2 inch. After that, you're looking at the local conditions you set up. Shallow melts can be dicey.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #8  
Old 07-14-2018, 08:24 AM
Dave Bross Dave Bross is offline
Registered User
 
Join Date: Apr 2002
Location: Archer FL(near Gainesville)
Posts: 2,943
Dave Bross is on a distinguished road
Good point on water in the chemicals.

I could only get consistent results in small batches by cooking the water out.

That would be the chemicals that gain and lose water from the atmosphere, carbonates mostly.
__________________
Art is not a thing...it's a way.
Reply With Quote
  #9  
Old 07-14-2018, 09:06 AM
Steven O'Day Steven O'Day is offline
Registered User
 
Join Date: Jun 2002
Location: portland oregon
Posts: 296
Steven O'Day is on a distinguished road
Yeah water is a problem. I wonder if a moisture meter could give an accurate enough reading. Plug the figure into a simple spreadsheet and adjust the weights accordingly.
Reply With Quote
  #10  
Old 07-14-2018, 12:10 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,278
Pete VanderLaan is on a distinguished road
Fritz had me do that in a simple way. Take 100 grams of each material and put that in the annealer at 250F for four hours. Weigh it again. If it now weighs 97 grams, you can do the math.

Stupidly simple.

2% moisture in silica can be easily attained actually. That would mean that two pounds of water are in every 100 lbs of silica. Quite a lot and adequately enough to throw most calculations. The reason I don't like those small samples is the coupling of the moisture issue with basic accuracy at the scales. The larger the sample, the less impact these deviations matter.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #11  
Old 07-14-2018, 07:02 PM
Steven O'Day Steven O'Day is offline
Registered User
 
Join Date: Jun 2002
Location: portland oregon
Posts: 296
Steven O'Day is on a distinguished road
I remember that trick. I'm running 30 or 40 samples at a time so it's impractical to mix large quantities. Ceramic glazes are a lot less critical than glass and the small samples are a good starting point.
Reply With Quote
  #12  
Old 07-14-2018, 08:42 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,278
Pete VanderLaan is on a distinguished road
when I get fresh supplies of hydrophyllic stuff like potash, once the big bag gets opened, it all goes into zip loc freezer bags.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #13  
Old 07-15-2018, 02:05 PM
Dave Bross Dave Bross is offline
Registered User
 
Join Date: Apr 2002
Location: Archer FL(near Gainesville)
Posts: 2,943
Dave Bross is on a distinguished road
An old Tuna can or a pyrex custard dish are ideal size for the moisture check.

I accelerate the process by cooking the samples in a toaster oven at full throttle.

How to know when they're done? Pull them and check the weight until there's no more change.
__________________
Art is not a thing...it's a way.
Reply With Quote
  #14  
Old 07-18-2018, 07:44 PM
Jeff Wright's Avatar
Jeff Wright Jeff Wright is offline
Registered User
 
Join Date: Apr 2002
Location: Milan, Michigan, USA
Posts: 222
Jeff Wright is on a distinguished road
My first results are very encouraging but the pots boiled over and made a mess!

How much space should be left to prevent this?. Are there any additives that can reduce the foaming?. I've heard that adding 2% Antimony helps with fining but noting about the foaming.
Reply With Quote
  #15  
Old 07-19-2018, 07:41 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,278
Pete VanderLaan is on a distinguished road
Foaming depends entirely on what you are trying to melt and you never said what that was. 2% antimony would be a very high percentage of the material unless you were actually looking for a grey glass.
Antimony does not inhibit foam nor does anything else. It's the result of oxygen ( or possibly something else) liberation in a mix. Antimony is a reducing agent and does have a variable valence but it would not do what you think it might do.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #16  
Old 07-19-2018, 09:40 AM
Jeff Wright's Avatar
Jeff Wright Jeff Wright is offline
Registered User
 
Join Date: Apr 2002
Location: Milan, Michigan, USA
Posts: 222
Jeff Wright is on a distinguished road
Got it one the antimony. Color was a deep yellow/amber color. 6% White Cerium (99.9%) and 6% Titantium Oxide. Wonderful color but made a mess. I think I'll back down to 4% for use in castings.
Reply With Quote
  #17  
Old 07-19-2018, 02:11 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,278
Pete VanderLaan is on a distinguished road
without telling me the source materials, I would suspect the amber is coming from some sort of sulfate or perhaps straight sulfur. Sulfates at (03) are indeed gassy. It's a pretty weak bond. I don't see how you get rid of the foaming during the charge unless you change the source on how to make amber. I suppose carbon or cadmium would do that but it still won't be fun. Bigger pots help.
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #18  
Old 07-19-2018, 04:46 PM
Jeff Wright's Avatar
Jeff Wright Jeff Wright is offline
Registered User
 
Join Date: Apr 2002
Location: Milan, Michigan, USA
Posts: 222
Jeff Wright is on a distinguished road
Source - Cerium came from HIS and the claim it is 99.9% pure. The Titanium cam from Standard Ceramic supply. I wondered about the sulfur. Bigger pots are in my future.
Reply With Quote
  #19  
Old 07-19-2018, 07:22 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,278
Pete VanderLaan is on a distinguished road
Cerium as a colorant with Titanium has always been a hard grasp as a color. The price is currently, notable. To be making it an initial foray into small batch color is really a hard row to hoe..
__________________
Where are we going and why am I in this basket?
Reply With Quote
  #20  
Old 07-19-2018, 08:41 PM
Peter Bowles Peter Bowles is offline
Registered User
 
Join Date: Sep 2002
Location: Breadalbane, Tasmania
Posts: 619
Peter Bowles is on a distinguished road
If you can mix well, you can add a known percentage (1%) of colouring oxide to say 10kg of silica, and then use a proportion of that mix to the remaining silica and batch materials. Spreadsheets will help enormously.
Whenever I've done small melts I mix the oxides into an initial amount of equal batch, then an equal amount again, and again, and again - basically doubling each time - till all done.
Getting the oxides equally distributed through a batch takes a bit of consideration for measurable and repeatable results.
Reply With Quote
  #21  
Old 07-19-2018, 09:03 PM
Peter Bowles Peter Bowles is offline
Registered User
 
Join Date: Sep 2002
Location: Breadalbane, Tasmania
Posts: 619
Peter Bowles is on a distinguished road
Cerium glasses will show a pleasing violet fluorescence under uv.
Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump


All times are GMT -5. The time now is 05:23 AM.


All published comments within these message boards are the opinions of its contributor and does not represent
the opinion(s) of the owner(s) of this website. Please see the Terms of Use file for more details.

Books to Help Artists Avoid Online Scams: Top 10 Email Scams | Social Media Scams

Powered by vBulletin® Version 3.7.2
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
CraftWEB.com. Opportunity Network. 2008. All Rights Reserved.