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Rockhopper

Member Since 16 Dec 2012
Offline Last Active Jun 28 2014 11:52 AM
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Posts I've Made

In Topic: Struggles Developing Clay Body From Local Clay

27 April 2014 - 05:04 PM

More testing completed... and more confused than ever..

 

I mixed four variations on the previous recipe - two with a little betonite added, and two with OM4 - trying to stop the leakage that occurred with the last test.  I made two identical pinch-pots from each, bisqued them all - then fired at ^6 one glazed, one un-glazed of each variation.  Then did 24hr soak + 2hr boil on the un-glazed

 

Mix (balance 'dug clay' approx 40%) Absorption EPK 35, Flint 15, Spar 8  +Bent 2 1.47% EPK 35, Flint 15, Spar 10  +Bent 2 1.47% EPK 34, OM4 3, Flint 15, Spar 8 5.88% EPK 32, OM4 3, Flint 15, Spar 10 5.88%

 

I filled all of the glazed pots with water & set them on a paper towel.  Two leaked, and two did not.  In less than an hour, there was water on the towel under two of them - and the water level in the pot was noticeably lower.  The other two had no water on the towel several hours later.

 

 

Herei's where I get confused:  The two that tested at < 1.5% absorption unglazed are the ones that leaked.  The pots that tested over 5% absorption unglzed are the ones that did not leak.  (No chance I mixed them up... each pair of test-pots was clearly marked as they were made.)

 

The glaze (floating blue) looks great on all four - no visible pinholes, crazing, etc.  I'm not really surprised, based on the absorption tests, that two of them leaked - but I would have expected it to be the two with the higher absorption.  Apparently I've still got a lot to learn.

 

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In Topic: Middle Of Kiln Is Overfiring

02 April 2014 - 05:30 PM

I'm still working on getting proper electrical hookup for my kiln, so can't speak from personal experience - but I've done a lot of reading in anticipation of troubleshooting such issues when I do get it plugged in ...

 

It seems that, even in an otherwise empty kiln, if your sitter is shutting off with a 3, but you're not even bending all of the 2's, your sitter may not be adjusted correctly. 

 

What did the '3' on your sitter look like when it shut off ?  Below is a pic from a Dawson kiln-sitter manual.  If your sitter cone looks more like the one on the left... it could suggest that the "sensing rod" is either bent, or out of adjustment - causing the sitter to trip prematurely. (A bent rod could also stick - causing it to trip late.)

 

You said it has 5 switches - are they all simple on/off switches, or do they have high/low options?  Doing a 'staggered start' (not turning all on at the same time) - or, if they're adjustable (high/med/low), not setting all to the same level - might help you balance the temps.

 

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Also... any chance you accidentally put a 2 on the sitter for your test, instead of a 3 ?  (Sorry, my tech-support background makes me ask those 'is it plugged in' sort of questions.)


In Topic: Struggles Developing Clay Body From Local Clay

15 March 2014 - 09:46 PM

Have you tested vitrification/ absorption of fired un glaze piece?

The leaking possibly leans towards under vitrified body.

It could be other things.

Did you try same body with more spar, or replacing some if not all with nephsy.

 

 

My testing method so-far has been to mix small batches, and make two arch-shaped tiles from each.  Both tiles are bisqued at ^04, then fired at ^6 - one glazed & one un-glazed.  Have tested absorption (24hr soak + 2hr boil) on all un-glazed tiles that survived ^6 firing. 

 

My scale only weighs in whole grams, so not real precise on the relatively small tiles (35g dry) - but the previous batch, using 10% spar, showed the same weight after soak + boil as they did dry, indicating they absorbed less than 1g  ( < 2.8 % ).  I backed the spar off a bit for this batch, because the previous tiles had a bit of sheen to them, and I was afraid they might still be a bit over-fired.  This batch, with 8.5% spar, absorbed around 7% :(  so.. it looks I'll go back to 10% with the next batch.

 

Interesting you mention Gold-Art.  I did some tests a while back adding various combinations of GA + EPK, OM4, spar, & silica, and they were some of the worst results I've had (although all were still 60% 'raw' clay).  Following John B's comments to my previous post, I've adjusted to using 40-45% raw clay, and getting much better results - but haven't tried the GA again.

 

Aside from possibly increasing vitrification, what impact would GA have on plasticity ?  The current blend throws OK for me, but is not as smooth when wedging, etc, as the comercial bodies I've used.  I definitely don't want to make it less plastic.  What about adding bentonite ?  I know it's sometimes added to improve plasticity - would it also affect vitrification ?

 

 

BIG congrats on slugging it out this far!!!!
It looks super good and promising.
Let me know if you need help testing for vitrification/absorption. Which I think should be your next in process.

Welcome to the "I made my own clay" club.

 

Thanks!  I know there are plenty of folks out there scratching their heads, wondering why someone would put the time & effort into making their own clay when "store-bought" clay can be had "dirt cheap".  If I were trying to do this for a living, I would probably agree with them - but as a hobbyist, short of taking advanced college classes, I would never have learned this much about clay if I only used store-bought.  (And, besides, I think it's pretty cool that I'll soon be able to make useable mugs, etc. with the same creek clay I played with as a kid. :) )


In Topic: Struggles Developing Clay Body From Local Clay

15 March 2014 - 02:05 PM

Update:   after much trial & error - 60+ recipe variations, 100+ test tiles, and failed pots ranging from crumbling to melted - I have a useable clay body.  Still need to tighten it up a bit before I can use it for vases & such (paper towel placed under bowl filled with water, gets damp pretty quickly) - but at-least my pots aren't coming out of the kiln looking like lava :)

 

Current mix;  Local Clay 41.5%, EPK 35%, Silica 15%, Custer Spar 8.5%

 

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In Topic: Source For Kiln Info / Manuals ?

09 March 2014 - 01:47 PM

Nancy-

 

The controls are split into 3 sections, although the kiln itself is physically two sections - a two-ring base about 18" high with a removable 9" high ring on top.  (The label that says 1700w is on the top ring.)  

 

It's single-phase, & has a 30-amp 'dryer cord', with the ground connected to the control-box.  (Another reason I was confused by the 7amp label.)  I've done a lot of electrical work over the years, and will definitely be sure wire/breaker/outlet are 'up-to-snuff' before I plug it in.  I will probably use wire rated for 40amps, with 30amp breaker just to be extra safe.

 

As mentioned in my last update, am now almost certain the 1700watts/7amps label is for the upper ring only.  Below are pic's of the kiln, with close-ups of the label and sitter.  I was able to download a manual for an LT-3 sitter from VulcanKilns.com - and it is close enough to the LT-4 to cover what I need to know for the sitter.

 

I would still like to find instructions for the rest of the controls - and recommended firing schedules (what settings to use for what cone-temp & how long at each setting.)

 

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PS - The wooden platform you see in the pic is just a temporary home to make it easy to move around in my garage until I build a metal stand ...  I have no intention of plugging it in until it's on a suitably heat-tolerant base. :)