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Rockhopper

Member Since 16 Dec 2012
Offline Last Active Yesterday, 07:30 PM
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Posts I've Made

In Topic: Fired Too Much? Or Not Enough? Help!

08 January 2017 - 02:17 PM

Glad the re-fire was a success!

 

Yestreday I did a glaze fire and it came out perfect with the 8 hour shut off... today.. not so much!!!

 

Are you controlling the kiln shut-off entirely with a timer ?  As you're discovering, it's going to be very difficult to get consistent results that way.  There are a lot of variables that can influence the time it takes your kiln to reach a given temperature and/or cone stage.  How full and/or how densely your kiln is loaded can make a big difference.  A kiln loaded with several shelves full of small pieces will take a different amount of time than one that's fired with just one or two large pieces.  (Even voltage fluctuations in the electrical supply can affect the temperature generated by the heating elements.)

 

You don't have to have a fancy computerized controller, or even a kiln-sitter, There are several folks on here with way more experience than me, who fire without either - but - just like baking a cake, or grilling a steak, you need to know more than "how long has it been cooking", to properly determine when it's done.  They use witness cones, pyrometers, and/or have many years of experience that lets them judge the temperature of the kiln based on the color they see through the peep/vent holes. 


In Topic: Fired Too Much? Or Not Enough? Help!

07 January 2017 - 11:32 AM

The discussion of shut-off switches and cameras was interesting... but I'm wondering...  Is Holly still out there ?   Did she find a solution, and has been to busy to let us know - or did she give up when the thread went so far off topic ?

 

Holly - if you're there...  Did you figure out what happened ?  Did you try re-firing ?  If you did - what was the result ? 

 

How about the lack of white on the the trees in the kiln - were they really just almost "exactly the same as the other tree in the other picture" (with no white applied) - or was there more going on with the new batch than just the lack of glossiness in the green ?


In Topic: Glaze From Local Creek Clay - What To Add ?

31 December 2016 - 11:00 AM

 

Like clay, glaze can have too much silica and not enough flux. I am betting that sandpaper feel is too much silica for the amount of flux. Have you sieved your clay? Is it actually clay or is it silt? Most native clay I have dealt with has too much sand (silica), and this sand is in particle sizes too large to melt down in a normal firing. Hence the sandpaper finish.

If your "clay" has too little clay (ie, kaolinite, meaning actual clay particles) then you will struggle to get it to work as a clay, either in glaze recipes or clay recipes.

When you put some slip of this clay on a plaster bat, how fast does the water leave it? If it leaves fast, then it is silt.

If you can, and if you can be bothered, the best thing is to get it tested in a lab to see what the chemical makeup is.

 

 

Definitely lots of sand before sieving.  My first attempt to throw with it was like grabbing hold of a drum-sander.

 

It's been sieved several times - starting with 1/4" hardware cloth to remove the 'big stuff', then some window screen (16 mesh), a nylon paint-strainer bag, and finally, with an 80 mesh - .0055 - screen.

 

Poured some onto plaster, along side some casting slip and some Standard #112 - it dried faster than the casting slip, but about the same as the #112. (Can't say for sure I had same water percentage in each to start with - just eyeballed the consistency.)

 

Would actually like to have it lab analyzed (if I can afford it) - but have no idea where to go for that.  I've looked a little bit, and so-far the labs I've found do soil testing for agricultural purposes (pH, etc.) - or they'll test for presence of lead or other toxins - but don't do actual content breakdown.


In Topic: Glaze From Local Creek Clay - What To Add ?

31 December 2016 - 09:49 AM

Custer can certainly be used.

 

 

I want to see if I can develop it into a glaze.

My recommendations were based on your comment.

 

 

I spent over a year, trying various combinations of EPK, OM4, Feldspar, and Flint,

You need a higher plasticity clay: other than what you have used. I would try FHC (Foundry Hills Creme), Plastic Vitrox (PV clay), or additions of bentonite (small percentages.)

Nerd

 

Thanks Nerd.  Your input is appreciated - I am definitely aiming for a glaze this time around.  My comment about trying various combinations was in response to Mark's post that local clays require "lots and lots of testing".  Not sure if FHC or PV are available locally, but will keep those in mind if I decide to make another attempt at a clay body.


In Topic: Glaze From Local Creek Clay - What To Add ?

30 December 2016 - 12:30 PM

The color is very nice. You could use Nerd's suggestion but do a test in increments of 5% of the silica and Neph Sy.
Begin with 5 silica and 10 NS and increase. You may have to test again to get the right ratio, Texture is determine by the ratio between the silica and the clay.
Marcia

 

Marcia -  When you say 'begin with 5 silica and 10 NS' - are those numbers ( a ) percentages of the total, or ( b ) percentages to add ?  From what I've read elsewhere about glazes, I'm guessing it's ( a ), since ( b )would make it approx 4% silica and 8% NS - but thought I should ask, just to be sure.

 

Examples:

a )  85g clay + 5g silica + 10g NS = 100g total

 

b ) 100g clay + 5g silica + 10g NS = 115g total