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Member Since 16 Dec 2012
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#129842 Sinter Firing

Posted by Rockhopper on 20 July 2017 - 06:03 PM



It still seems to me that by the time you get to sinter-point, some proper work has been done to the glaze, and real irreversible changes have occurred, which makes a (theoretical) difference to the amount of heatwork you need to finish the job off. (It's entirely possible I'm wrong in both fact and terminology - what a surprise that would be...)


I'm thinking you could test that theory by placing some witness cones in the kiln during your sinter-firing, then put the same cones back in the final firing (as close as possible to original location) along with a fresh set of the same cones.  Then compare the two sets and see if the sintered cones bend noticeably farther than the un-sintered ones.  

#127631 Bulk Corks For Jars

Posted by Rockhopper on 04 June 2017 - 01:00 PM

Have never bought from them, and don't know how their prices compare with what you've been buying - but http://www.widgetco.com/corkseems to have about any shape/size of cork you would need.

#127630 Almost

Posted by Rockhopper on 04 June 2017 - 12:53 PM

Studying the two pots next to each other I noticed the handle on the teapot was a whole lot drier then the body. I also noticed that the body on the mug was also drier than the body of the teapot.


The only difference I can see is I kept the lid on the teapot while it was drying. I'm thinking that the teapot body isn't drying as fast because it is a closed form while the handle is out there exposed to more air and shrinking quicker.



What has me wondering is the spouts haven't split from the body, maybe even though there is a small opening at its end its still a closed form, or maybe the moisture from the body is moving out through the spout keeping it moist enough not to crack.


Having the lid on the teapot will definitely cause it to dry slower than it would uncovered. (It will also dry from the outside in.) 


It looks like your spout is thrown - which means it may be starting out with a moisture content closer to that of the pot.  It is also probably more uniformly moist throughout than the pulled handle, which may have more moisture near the surface, and less toward the 'core'. 


I always cover a mug (or any pot with an attached handle) with an upside-down bucket, for 12 - 24hrs after attaching the handle.  This slows the drying, and allows the moisture to equalize throughout the assembled piece. It may not be practical in a production setting, but as a hobbyist that typically only throws 6-8 pieces in a session, it's easy to do.

#126826 Help! Newbie Struggling With How Much Water?

Posted by Rockhopper on 16 May 2017 - 09:32 PM

I also think your clay is probably too stiff.  When the clay is stiff, you have to press harder to move it.


I recently ran into this with some 'left-over' stoneware clay that had been given to me. The harder I pressed, the more water I needed to keep my hands lubricated.  The outer layer starts turning into slip before the rest of the lump is soft enough to really work well.  A two-pound ball of clay soon turned into a one-pound lump, and a splash-pan full of slip (not to mention the coating on my hands & fore-arms).


There are lots of ways to add moisture to your clay.  I use a method similar to what Marcia suggested.  I usually start with 3-4 pounds and slice it into several 1/2-inch thick pieces.  Then, Instead of dipping and letting each slice sit, I sponge a little water onto the top of each slice, and "stack & slam".  Process is repeated until the clay is uniformly moist.


It's difficult to describe the correct softness - but it's amazing the difference it makes.


PS - If you haven't heard of "stack & slam" wedging check out this article and the accompanying video. There are other variations on the technique, but this gives a good explanation of how it works.

#122256 Hummingbird Feeder Spout Placement

Posted by Rockhopper on 13 February 2017 - 06:06 PM

Definitely do NOT want a 'vent'.  Regardless of what shape your feeder is, it needs to function as a bottle - with the only opening being the one that you put the tube/cork into.


The reason the tube works is that air cannot get into the container except through the tube.  If you have a vent hole, it will let air in, and the nectar will run out as fast as the air can come in.

#119415 Glaze From Local Creek Clay - What To Add ?

Posted by Rockhopper on 29 December 2016 - 07:14 PM


As a simple base line; start with: 25% native clay, 20% silica, and 55% Nep SY.  (8.58 total alkali - molar)





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.


The best answer is probably "try it and see"... but would doing the same with Custer Feldspar, instead of NS, be an option worth trying ?  (I already have some Custer on-hand, and would have to go buy some NS to try it.)

#119412 Glaze From Local Creek Clay - What To Add ?

Posted by Rockhopper on 29 December 2016 - 07:01 PM

Making clay or glaze from local materials requires lots and lots and lots of testing


No doubts about that Mark...


I spent over a year, trying various combinations of EPK, OM4, Feldspar, and Flint, added to my base clay, trying to get a 'wheel-friendly' body. (Didn't have my own kiln, so would mix several small batches, make some test pieces, then wait a week or two for the studio owner to fit them into a firing.)  I learned a lot about clay in the process - but when I reached the point where "my" clay was no longer the primary ingredient, I felt like I was just adding some of my clay to 'other stuff', and gave up.  (In my mind, it was OK to add stuff to my clay to make it work ... but when it was the other way around, the end result was no longer the clay from 'my creek'.)

#54737 Struggles Developing Clay Body From Local Clay

Posted by Rockhopper on 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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#43800 Struggles Developing Clay Body From Local Clay

Posted by Rockhopper on 06 October 2013 - 08:29 PM

These two show the wide surface, middle portion of the two pieces.  4) Shows tan and RR side-by-side and overlapping in center; 5) un-glazed strip


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#43799 Struggles Developing Clay Body From Local Clay

Posted by Rockhopper on 06 October 2013 - 08:26 PM

Here are some close-up pics.  Not quite pro-quality macro, but as good as it gets with my Canon powershot..


The first three are cross-section of broken test-strips.  1) Un-glazed;  2) RR end of glazed piece; 3) Tan end of glazed piece.  (2 & 3 are opposite ends of same piece)


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