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#115567 Silica Sand For Use Under Slabs

Posted by perkolator on 02 November 2016 - 12:33 PM

12"x12" isn't that big of a slab.  dunno what firing schedule you're using but likely it's too fast.


slabs and similar work with large flat surface areas against a shelf (like slabs, and big platters/pots without a foot trimmed into it) tend to have two main issues with firing.


-One is that they are a big surface area, sitting flat against a shelf, thus the heat cannot easily penetrate to the bottom, center, of the clay.  Because it was cooler than everywhere else during the time you were candling your kiln, by the time you go to your next stage of firing, this cool section kinda rapidly heats up and thus you get blow-outs. Raising/elevating the piece will help tremendously. Also slow down your firing to compensate for lack of heat penetration.  Kinda the same concept if you were to stack a really tight, low height shelf in the bottom of your kiln - the heat can't penetrate very well.


-Second issue is more likely with larger work than the scale we're talking about, and the problem is usually cracking due to the friction and drag caused by the physical weight of the mass as it's trying to expand/contract in the kiln.  Something under the piece



Yes, silica sand can work if you need to sit it flat.  Grog will also do the same thing.  Putting a layer under your piece will act as ball bearings and facilitate the movement as the clay expands/contracts.  Since it's not a solid, it will also allow moisture and heat to pass through the interstices and make its way to/from the bottom.  Another alternative is raising the piece on pieces of broken kiln shelf or clay pucks.  Most of the time with big work, I use either the broken shelf bits or balls of kiln wadding (1/3 each: grog, silica, clay) - they do the same thing, but they have one main factor that makes me go toward them before loose sand/grog......Grog/sand can fall through the shelf crack/joint to the work below, the wadding stays put.  Another benefit to the wadding and sand is that they will self-level out which is great if your kiln shelves aren't perfectly flat, but your piece was built on a flat surface.


Yes, slabs fired at an angle on their side can definitely warp.  Depends on how thick/thin, how heavy, how big, the temp you're firing to, etc etc.


I lean stuff on soft brick all the time as long as there's no glaze.

#114519 Quartz Inversion

Posted by perkolator on 10 October 2016 - 04:02 PM

Well yes, the more mass in the form, the more they are susceptible to the forces of nature/physics/kiln firing/etc.  Hard to give specifics since it varies so much depending on what it is, how it was made, etc etc.


As for quartz inversion - 2% expansion doesn't seem like much to a little cup or plate, but to a 6ft tall sculpture with a 1" thick wall will definitely have some concern and you may have to make some big changes to accommodate making that item.  With bigger work it's inevitably going to be "moving more" as things shrink especially.  You actually have to engineer your sculpture to accommodate certain shapes, kiln firings, etc etc.


For example, everything made from clay will shrink to some degree and obviously clay can be heavy.  You may not be able to perceive the shrinkage from your average cup/mug, but if you scaled it up to a 24-36" diameter vessel you're definitely going to be able to see the shrinkage as it will be obvious at this scale.  Big heavy sculpture often gets vertical cracks originating from the foot, likely due to the heavy weight of the form and the friction on the work-surface as the piece dries, this continues as it fires and shrinks again.  Big work makes "walls" in the kiln that make heating uneven sometimes, so how you stack your kiln will likely effect the work too.  Example of that might be firing several long-necked forms - if you cannot place these centered in relation to the heat source, it's likely the uneven heating will warp the piece and it will lean toward the heat source since that side shrinks more.


If you fire very conservatively your chances of surviving these forces are much much higher.  Obviously you won't be able to fire big stuff on a fast kiln firing schedule, sometimes you even have to down-fire your work so it doesn't get dunting cracks. Keep in mind that my studio operates outside the box of your typical ceramics studio.  Most of our work is fired earthenware temp, with a forgiving stoneware clay body...oh yeah and did I mention most of our stuff is once-fired?!  Most of my gas kiln firings with big stuff takes about 1 week turnaround for firing - 1-3 day drying/pre-heat, up to 24hrs to fire, 2-3 days to cool.  Go slow from pre-heat to quart inversion.  Remember, it's not only quartz inversion to be concerned with...all ceramics still have chemical water that needs to come out too...so if you go too fast with a 1" thick piece of clay...boom....

#113543 Studio Safety

Posted by perkolator on 21 September 2016 - 04:43 PM

Silica dust is carcinogenic, try to avoid breathing any clay or glaze materials particulates whenever possible.


Some things that come to mind for general studio safety:

- Cheap disposable or reusable chemical gloves for glaze handling and misc hand-protection needs.

- Chem goggles/eye protection for cleaning out glaze containers or flying debris from chipping/grinding fired glaze.

- CMC gum in glazes to keep glaze from powdering off when transferring glazed work to kiln.

- Particulate-rated NIOSH respirator for general studio use.  I like 3M N95 8210 particulate respirator.  Use 8011s if you have a small face.  You can get higher filtering, but they are hard to breath through IMO.

- Leather gloves for handling hot wares from kiln, sharp edges of wares stuck to kiln shelves, etc.

- Try NOT to dry sweep, use wet-cleanup methods whenever practical.  Sponge it down, mop it.

- If dry sweeping use a respirator, provide ventilation, use floor sweeping compound if you have it.

- Obtain MSDS info on any chemicals you have in your studio and ACTUALLY READ IT so you know how to handle, transport or dispose of your material, etc.

- Clean up studio daily.


In regards to your mold issue, I dunno what to do there.  Sounds like your studio is too well sealed.  You may consider some sort of ventilation for the room.  Also, I don't know how you store your wet clay or wet in-progress work, but try to isolate it with plastic or store it somehow so the moisture doesn't raise the whole room's humidity.

#113541 Grinding Excess Glaze Drips

Posted by perkolator on 21 September 2016 - 04:31 PM

GOOD: chisel, silicon carbide rub brick, white stilt stone, etc.

BETTER: bench grinder, angle grinder, dremel, cutoff wheel, diamond blade, etc.

BEST: diamond bits -- look at what CI Products offers - they have fancy grinding discs for putting on bats for use on potters wheel, small bits for rotary tools, hand sanding/honing pads, diamond grinder accessories, etc.

#113538 Any Good Extruding Tutorials?

Posted by perkolator on 21 September 2016 - 04:26 PM

I'd say just start using it and learn from any mistakes you make.  Clay consistency is HUGE factor when extruding clay.  Good luck!

#110542 Hard Time With Extruder..not Extruding?

Posted by perkolator on 25 July 2016 - 06:12 PM

Did you get this figured out?  Which Bailey extruder system do you have?


We have 3 extruders in my studio - manual Bailey wall mount, free-standing Bailey pneumatic, and a custom 14" hydraulic extruder.


Does your extruder function without any clay in it?  Obviously it should.

If it's the pneumatic extruder - you have to press the foot pedal and let air through in order to see any reading on the regulator.

I don't really know how you can jam up a manual extruder unless the plunger gets stuck/wedged from an object or misalignment.


Soft clay is the key to getting clay to come out, less resistance for certain shapes.  Lubricating with water on the clay/in the hopper helps tremendously.  Bailey recommends spraying WD-40 on the wood die plates when you first start using them, i've noticed it help slightly.  Beveled edges seem to help on some shapes too.

#110160 Getting Fail Message On Skutt Kiln

Posted by perkolator on 15 July 2016 - 03:29 PM

Glad you got it figured out.  

I have all Skutt electrics in my studio.  The new Skutt control boxes are awesome, I have only one (all others are 20 years old!!!) - but it allows you do do diagnostic stuff from it.  Skutt website has tech info and links to videos on how to test and troubleshoot.  Also, their kiln techs DO answer the phone and will help you out with questions.

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#110155 Fixing Cermaic Tiles To Make Framed Work

Posted by perkolator on 15 July 2016 - 03:00 PM

For something like this you could use almost anything.  Hot glue, E-6000, silicone caulking,  liquid nails, etc.  Heck, you can even just use those staples/brads to hold it in the frame.  Just make sure the FRAME is up to the task.

#104115 Reclaiming Large Volumes Of Slop

Posted by perkolator on 24 March 2016 - 12:16 PM

I'd personally end up doing what I saw in a Korean onggi video if I didn't want to deal with dust or small 5-gal reclaim batches.  If you can do it, store your reclaim in trash cans and wait until the weather clears (or do it somewhere indoors i suppose).  They can be outdoors since you said no space inside.

Simply pour/scoop out your reclaim slurry onto a big plastic sheet/tarp, let it evaporate to the consistency you like, then cut strips and roll it up like sod grass.  Run these through your pugger and store them/use them.  To me it seems like much less work than doing smaller batches.

#102272 Does Anyone Recognize This Low Fire Glaze?

Posted by perkolator on 19 February 2016 - 12:57 PM

Are you looking for a commercial glaze or a recipe for a glaze that will do that effect?

#101856 Cones Do You Bisque The Packs

Posted by perkolator on 11 February 2016 - 06:32 PM

I would never personally bisque cone packs.  My theory is that when you re-fire ceramics the "maturation temp" so to speak goes down a little each time you re-fire.  So if ^04 was originally at 1941* the first time, it might be 1925* the second time, etc.  I'd never want to compromise the device that is measuring the maturation temp in the kiln, so I'll never bisque cone packs.


The standard is to either make cone packs in advance so they are bone dry, or to perforate the clay with hundreds of pin holes to allow steam to escape quickly.  In our studio we simply use kiln putty/kiln wadding to embed our cones in, instead of regular clay.  It's the same material we use between bricks and shelves in our stack, since our biggest two kilns are a shuttle and a trackless, with literally tons of weight on them and plenty of vibrations - the wadding helps dampen vibrations and also level shelves against bricks.  I've stuck freshly made cone packs and kiln gods and small wadding sculptures directly into all types of firings and have never seen it crack, split, blow up, etc.  It's an expensive material since it's a consumable that's only used for firing.


Kiln wadding recipe:

1 Silica

1 EPK/Clay

1 Grog

#101849 Materials For ^6 Copper Red Oxidation

Posted by perkolator on 11 February 2016 - 06:07 PM

I second trying a non-ceramics supplier for their silicon carbide.  Lapidary supply, glasswork suppliers, maybe sandblasting, etc should all carry it.  I want to say our print lab gets their SiC for grinding/polishing lithography stones from a print/litho supplier.  


The only issue I see with buying from a non-ceramics source is they might categorize the SiC based on GRIT size vs MESH size. I'm not sure on the conversion, there should be info online about this.  I know our print lab has as fine as 800 grit I think, which is pretty fine.

#101790 Adding A Frit To An Oxide To Create An Oxide Wash

Posted by perkolator on 10 February 2016 - 08:21 PM

You can use either Frit, Gerstley Borate, or make an underglaze with equal parts clay color and flux.  Frits, being fired material usually leave a gritty/sandy texture to the wash, some people use CMC, laundry starch, karo syrup, etc to help.  Usually I use GB and CMC gum solution, sometimes add a little bit of EPK in it too.


Look up Linda Arbuckle's majolica notes, she's got a lot of suggestions for combos of washes.  Most are by volume, not weight.


Here ya go: 



#88012 Mold Making

Posted by perkolator on 29 June 2015 - 05:39 PM

DO NOT use grease, WD-40, vaseline or any other oil-based substance like suggested above, as your mold release.  The whole point of using plaster is to take advantage of the capillary/wicking action of the material, to pull water from the clay and set it up faster - if you go and use something oil-based as a mold release, you've now clogged the pores and severely diminished capillary action, if any at all.  


Use actual "mold soap" or purelube/greensoap, which are the products that should be available from any ceramics supply.  Alternative is diluted Murphy's Oil Soap.

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#80294 The Dirtiest Job In Ceramics

Posted by perkolator on 28 April 2015 - 01:59 PM

Cleaning sink trap has got to be #1 only based on the smell.


A very close contender is making a batch of clay with a super-smelly reclaim barrel which smells as bad as a sink trap, because it's full of dead skin cells, newspaper bits, etc and has been sitting in the sun for a few weeks....and you're putting your bare hands in it...and your head goes into or very close to the trash can because you're reaching to the bottom...at least with the sink trap you can use a wet-vac and cover your nose with the free-hand.