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Tom the idea with the plasticizer was just to reduce shrinkage from drying.

For the Starlite he later added borax which made it much less flaky.

VincentG wrote: ↑Fri Apr 07, 2023 1:42 pm Tom the idea with the plasticizer was just to reduce shrinkage from drying.

I've looked into plasticizers for porcelain clay just now.

Apparently the type of clay I have, which I chose on the basis of firing temperature, on the assumption a hotter firing clay would handle high heat in an engine, would often be mixed with a plasticiser. It seems porcelain clay alone is prone to cracking.

There are pre mixed clay formulas. that might be more appropriate for this project.

Plasticisers for clay vary and the whole subject becomes rather complicated. This article for example, goes on and on and there seems to be no simple answer.

https://digitalfire.com/glossary/plasticity

Well I think I was probably on the right track earlier:

viewtopic.php?f=1&t=5415&start=90#p18982

A combined clay/paper product whipped up in a blender.

As it turns out, this is actually a thing that has been around and used by sculptors for years, though a fairly recent innovation used primarily with porcelain.

It consists of simply making ordinary paper pulp in a blender in the usual way and mixing it together with porcelain slip, which is just clay and water.

Called "paper clay" (two words) which is fired in a kiln, this is not the same as paperclay (one word) which is an air dried polimer. Though I have discovered this convention is hardly followed by anyone.

The paper fibers give the porcelain extra strength, make it much easier to work with, virtually eliminates cracking, produce a lighter weight product and this allows the porcelain (or other types of clay as well) to be formed into very thin and delicate shapes, like porcelain netting, long thin string-like shapes or even lamp shades.

The paper fibers just burn away when the paper clay is fired in a kiln.

The material, made into slabs, is also extremely easy to join together using the wet clay slip and paper fiber mixture as "super glue" to join pieces together and build structures. The paste globbed onto joints bonds the pieces together very strongly and almost instantly.

Fiber from ordinary newspaper is commonly used, but other plant fibers like flax or hemp work as well

The very thin and delicate little porcelain plates and translucent lamp shade in this video, for example are made using porcelain clay and industrial hemp.


https://youtu.be/Ylvvv0KEBes


There is a ton of information on the subject available, and artists/sculptors have been successfully using this "paper clay" technique for years already, teaching online courses and so forth. I don't know how I managed to avoid running into it before now.

This website has an exhaustive amount of information and is a kind of hub with dozens of links to other websites, artists, video etc.

https://amyleepottery.com/blogs/news/ge ... paper-clay

Generally following the instructions in this video::


https://youtu.be/B5xzidCCNU0


I made two batches of paper clay slurry

One using newspaper and toilet paper for the cellulose fibers:


And the other, just hemp hurd exclusively:


I tried using my paper making screen but the slurries are too thick and hold water too well. The water does not pass through the screen to drain the water out. The stuff just sits on top of the screen like a blob of jelly. So I poured it out on the canvas as I don't have any plaster slab.

My impression so far is that the hemp mixture is more runny. I had some difficulty keeping it from running off the edges of the canvas and had to turn up the sides to hold it in.

The newspaper/toilet paper mixture came out more like whipped cream or a foam, like shaving cream.

I was going to try some part hemp hurd and newspaper/toilet paper mixed but I kind of wanted to compare the results hemp fiber vs regular paper fiber.

My hemp hurd was obtained from hemptopia:

https://www.hemptopia.com/hemp-hurd-bale-15-kg-33-lbs/

This is not, I don't think, the kind of quality hemp fiber used for weaving fabric, just the coarse woody stem so I left it soaking in water in the blender overnight and blended it up repeatedly but it never reached the smooth frothy consistency of the paper fiber mixture, more like blending up water and toothpicks. Not quite that bad, but the fibers would come out of suspension rather quickly compared with the paper fibers which stay suspended in water almost indefinitely.

For this application, making a high temperature displacer, I'm not entirely sure if the coarser more woody fibers aren't actually preferable.

I can still try a mixture I guess, by just kneading together some of the paper clay from the two batches once they drain and dry out a bit. I'm not sure how long that will take on the canvas. It seems to be going rather slowly.

I was not very particular as far as proportions, but in general I used a higher percentage of cellulose fiber in my mixtures, more like 50-50 pulp / clay slip rather than the 30-60 recommended in the video.

It also, due to the more woody texture, required much more hemp, by weight, to blend up a volume of fiber slop.

The paper fiber bulked up or swelled up more quickly with less material putting more of a strain on the blender sooner than the hemp fiber which remained more watery.

That is the hemp fiber did not create so much of a thick froth, more like sawdust floating in water.

It's been six days drying the paper clay.

I'm sure the long drying time has been at least, in part due to trying to let it dry in the cool basement, as well as lack of a proper plaster drying table.

Though the mixture with the hemp hurd started out much more runny, it was actually probably too dry two days ago and I pealed it off the canvas two days ago, however the mix using the newspaper was still wet and sticky today, and is still probably too wet to work easily.

Still don't know which will work out better in the long run, maybe a mixture?

Anyway, the consistency of each can be seen in this video I just made and uploaded a few minutes ago:


https://youtu.be/ZrGbPe9yAeY

I just found my old Sunnytech LTD Stirling engine from more than ten years ago, in parts and pieces after it had melted down by running it on the top of my wood stove.

This was the engine that started me on this quest for high temperature engine components. The little thing was running quite impresively on the wood stove, up until the plastic and styrofoam started melting.

I just came across a bit of technical information I did not realize before now.

Kaowool blanket is produced from kaolin clay by the blowing process

https://www.distributioninternational.c ... cfbt6022kt

Kaolin clay is the main clay used for making porcelain.

Second attempt at making an extra large microwave kiln:


It came out satisfactory I think. Still need to wrap it with some kaowool.

This time I tried using a pyrex bowl coated with paraffin wax as a "release" to keep the kiln element from sticking to the bowl.

It did not exactly pop right out. I had to heat it inside the bowl to cure it, sacrificing the bowl in the process.

The wax burning off smoked a lot but fortunately I had the sense this time to take the microwave outside.

The kiln would not quite get red hot with the bowl, as the pyrex absorbs too much of the heat.

When I opened the microwave the pyrex bowl just exploded when the cold air hit it. Fortunately though, the silicon carbide shell survived.

Testing the kiln, without yet having insulation, it did get red hot, in spots. I think it should work OK but being so large it will probably take longer to heat up than a normal size microwave kiln.

Perhaps this could be useful at some point. Apparently paper clay can be reinforced with steel.


https://ceramicartsnetwork.org/daily/ar ... -Sculpture

Another interesting possibility; apparently paper clay can be sprayed with a hopper gun like stucco for large projects.

https://www.grahamhay.com.au/baker1998.html

There is at least one standardized commercially produced paper clay available known as "P'clay".

I just sent for a sample from this website:

https://www.clayimco.com/product/p-clay ... 2&limit=10

So I will be comparing this with my 2 diy versions of paper clay

I also sent for some high temperature kapton tape for wrapping kaowool insulation around the kiln which should be arriving soon.

After seeing this video:


https://youtu.be/P1VmIYheuU4


I was planning on using Kaowool and kaptain tape to insulate my kiln, but my dome shaped heating element shell seems a little too thin and fragile and seems like it would fall out if just wrapped with a Kaowool blanket, so, I came up with another plan.

I had experimented with making refractory and wondered if I could seal the dome within another dome made of some kind of refractory.

My first attempt at this was to use 50/50 plaster of Paris/perlite with a little waterglass. I've seen similar mixtures used for making a metal melting forge.

I thought the plaster and perlite mixture would probably not get hot in a microwave but would serve as a good insulation and also be strong and rigid enough to hold the fragile silicon carbide shell securely in place.

I tested this using one of the broken shards from my previous failed attempt at making a microwave kiln using a flowerpot.

https://youtu.be/06HTRZNcM-w


This seemed to work exceptionally well.

This is just a 900 watt microwave, yet the test piece heated up to red hot in less than 2 minutes. My workshop microwave is a few hundred watts more powerful. This is also inverted with no real insulation above the heating element, so I think this may work out.

As I hoped, the plaster & perlite remained cool and unaffected by the microwaves. The silicon carbide shell also held securely to the plaster.

The actual kiln coated with the plaster & perlite mixture drying in a bucket.


I added a bit more perlite to the mixture this time. But then it turned out rather watery, so put in a few more scoops of plaster to get it to a cottage cheese consistency. Still, probably something like a 40/60 mix plaster to perlite.

First fiber clay displacer, rolled out and cut to fit in a standard commercial LTD model engine.

Just trying to speed up the drying time before firing in the kiln, which turned out pretty good I think.

What's the final grams per cc of that substance after firing? Does it take a direct torch flame okay?