THE PARAGON XPRESS E10ABW

[Fire_assay_disciple]

Hello,

I am considering to by myself a kiln for fire-assay (cupellation) and wonder if you think that this kiln would be good for that? I am thinking about buying the model which includes "bead door" and "window", 1230 C.

http://www.electrickilns.co.uk/xpre.htm

Moreover, I wonder if the "bead door" would replace the need of drilling a hole for air-flow supply??

Any comments would be valuable. Thanks in advance!
Christer

 

[goldsilverpro]

I've never actually seen one, but the Paragons seem to be well made with adequate insulation thickness (seems to be about 2" - 2.25" thick on the one you're looking at.).

I don't like the way the door swings to the side but most box furnaces designed for pottery are made like that. When open, they are very hot to work around and you'll most probably need something to protect at least your left arm and possibly your neck and face from the heat coming from the orange-hot door. My last furnace was a #16 Vcella that opened to the side and I'll never, ever, own another one. With the smaller furnace you're looking at, it may not be so bad. I have used several fairly large Cress furnaces, where the door slides up, and they are much cooler to work around, since the hot inside of the door is facing away from you. With those, I could get away with a cheap plastic full-face shield and good welder's gloves for heat protection.

The purpose of having holes in the door and the back of the furnace is to allow some air to flow, from front to back (or, visa versa), across the top of the lead or bismuth in the cupels. The oxygen forms lead oxide on the surface, which slides off the rounded meniscus of the lead and is absorbed by the cupel. Without this oxygen, no lead will be absorbed by the cupel. With only a hole in the door, you will probably only be able to cupel some of the samples in the front row. I would definitely drill a 1/2" hole in the back, centered from left to right, about 1/3 of the chamber height measured from the top inside. I am assuming there are no elements on the back inside of the chamber.

How many cupels do you want to run at one time? After the furnace is hot, figure about 45-60 minutes per batch of cupels. Will you be running any assay fusions in assay crucibles? For karat golds, all you need is cupellation. For electronic components, ore, etc., you'll have to do a fusion first.

 

[Fire_assay_disciple]

Dear GoldSilverPro,

Thanks for taking your time to answer my questions.

I am thinking that it would perhaps be better to use this one, which has a vent hole on the top instead:

http://www.paragonweb.com/Xpress-E-12A.cfm

There is also an option to have a small window, you think that that could be helpfull to a beginer, or is it just as easy to open the door time to time and see how the cupellation progress? The maximum heat is somehow limited with a window, although it may still reach 1230 C.

You think that it could work that way with the vent hole on top?

I will protect myself from the heat with gloves and a face shield. Thank you so much for your exprtise, I will certainly consider to buy your book. I am reading the Bugbee book right now.

All the best,
Fire-assay disciple

 

[goldsilverpro]

Dear GoldSilverPro,

Thanks for taking your time to answer my questions.

I am thinking that it would perhaps be better to use this one, which has a vent hole on the top instead:

http://www.paragonweb.com/Xpress-E-12A.cfm

There is also an option to have a small window, you think that that could be helpfull to a beginer, or is it just as easy to open the door time to time and see how the cupellation progress? The maximum heat is somehow limited with a window, although it may still reach 1230 C.

You think that it could work that way with the vent hole on top?

I will protect myself from the heat with gloves and a face shield. Thank you so much for your exprtise, I will certainly consider to buy your book. I am reading the Bugbee book right now.

All the best,
Fire-assay disciple

It's hard to beat the Bugbee book. It's the one I grew up with. All the basics are there. As with all assaying books, it is geared towards ores and other mining materials, although there is a lot of info on bullion. The assaying chapter in my book is mainly geared towards electronic components and karat golds.

In some of the photos of the Paragon furnaces, they show a hole in the door (is that the sight-glass you spoke of?) that can be covered with a rotated disc of metal. If it's a hole and not a sight-glass, I would get one like that and then drill a hole in the back. You need 2 holes, an air inlet and an air outlet. Since the air is needed over the cupels, I can't see how a top hole would work very well. Some of these things were discussed on this thread.
http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=56&t=6090&p=53284&hilit=vcella#p53284

You don't need 1230C (2246F) for common cupellations. In rare cases, you might need that for fusions. If you find that there is too much heat leakage during certain hi-temp fusions, you might try carving hole plugs from a soft firebrick. Don't make them very snug (they can break easily) and make them long enough so you can easily pull them out.

With the Cress furnace, whose door is raised, I only had a hole in the back. For the air inlet, I simply raised the door a crack (say, 1/8") and held it open with a piece of something like a small chunk from a broken crucible. That worked better than a hole in the door, since the gap was across the entire width of the door and all the samples cupelled fairly evenly. Here's what the Cress furnaces look like.
http://www.lmine.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=LMS&Category_Code=cress_assay_furnaces

Most furnaces I've used had a digital temperature controller. They are more accurate, easier to use, and safer, in my estimation. Most cheaper models come with an analog controller that should not be left unattended. Although I don't know exactly why, I have twice seen runaway furnace meltdowns with these. Not a pretty sight. In these cases, the elements got hotter and hotter and, eventually, the firebrick melted around the elements.