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Indemnity4 t1_jb2zqez wrote

Same idea as bricks and mortar for building a house - the bricks are the structural support and the mortar is the fluid stuff holding the bricks together.

Same idea as adding grog to your clay.

Microscale, clay particles shaped like little flat overlapping discs. Place your hands over each other and then imagine 10 people all overlapping hands to do a big Lets Go Team! cheer. They are also charged like magnets. The water in the clay is phsycially separating the clay particles so they can slide over each other and be worked.

When you are working the clay it is wet and all the little charged discs are pushing each other away. However, when you are drying the clay (biscuit phase) or firing, the water evaporates. All those little charged discs start to be attracted to each other and pull together.

Some types of clay have what's called a "vitreous component" or a "flux" - it's just naturally in the type of clay, although it can be an additive too. It's stuff inside the clay that melts during firing and turns into glass. Sounds great, but the solid->liquid phase change is smaller volume so it makes little bubbles inside the clay wall.

Overall, the clay shrinks and pressure starts to build up in the walls.

The grog or sand is an inert piece of material that slow down shrinkage and reduces internal pressure in the clay structure.

Now, with this grog additive, during firing some of the clay melts to form a fluid glass that moves to fill in the voids between the solid grog. Other clay melts to fill that hole, and so on. You end up with a much stronger piece of clay with less shrinkage and much less likely to shatter to relieve that internal pressure.

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CJW-YALK t1_jb32dyc wrote

Unrelated: but on the subject of micro-scale clay particles…kaolin is a iron deficient white clay, relatively high in alumina…it’s used for all kinds of products. One use is paper, those same “hands” over lap each other and provide a smooth surface….if you’ve ever thought “man this paper is nice to write on” vs something like a napkin, your writing on the over lapped kaolin particles….(napkins, toilet paper etc are mostly tree fiber and absorb) …..heavy heavy application of kaolin can provide the slick feel of magizine at the extreme end, though many of them have moved to polymers

So next time your writing a note on nice smooth paper, remember your actually writing on dirt

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Jmazoso t1_jb342q9 wrote

Also, the anti diarrheal kaopectate got its name from one of its original ingredients —- kaolinite.

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CJW-YALK t1_jb3e24f wrote

Yep, but kaolinite was a filler mineral, it’s completely inert…nevertheless you’ll see people picking it up off the side of the road to eat raw from where it’s fallen off haul trucks

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Jmazoso t1_jb3wequ wrote

Not completely inert. It likes water, it bonds with water chemically due to its physical/chemical charge. It does swell somewhat when it does this, not to the extent that illite and montmorillionite do, but some. So it will make “stuff” less fluid.

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gristc t1_jb40z1s wrote

Don't leave us in suspense, what does it taste like?

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CJW-YALK t1_jb4wmbr wrote

Well….I routinely tasted it to determine its grit (sand) content in the field (I’m a geologist) …..it tastes like nothing, texture wise it’s like chalk until wet then it’s creamy…I was always tasting such a small amount and always focused on the sand part (rubbing on teeth) …..everything but the most pure stuff will have a sand content so eating raw kaolin will be unpleasant honestly

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black_brook t1_jb3roe5 wrote

That doesn't really explain what was asked though. How does the grog or sand slow down shrinkage?

Also how does having the grog or sand allow some of the clay to melt to fill in the voids? Why wouldn't that happen also without the grog?

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WazWaz t1_jb3ykr9 wrote

For the obvious case, there is less material shrinking. If the mixture is 50% grog, then clay that otherwise shrank by 10% should at most shrink by 5% since the sand won't shrink at all.

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[deleted] t1_jb413sr wrote

[removed]

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black_brook t1_jb44w0j wrote

Also "grog particles don't shrink" does not explain anything because clay partials don't shrink either. They condense by sliding together like u/Indemnity4 explained. I assume the grog particles must block some of the clay particles from sliding together and affect shrinkage that way, but that is only an unexpert guess.

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jeffersonairmattress t1_jb5udhi wrote

They sort of obliquely refer to it, but omitted the attraction of clay to the surface of the grog/sand particles- the clay would rather stick to each particle than allow gravity or other force to separate them. this bond is “fluxed” by moisture while workable (a pug or other milling process acting just like a mason back-buttering stone/brick/tile) but once smeared all over each particle, the drying phase doesn’t weaken the bond and the particles of sand are each captured by clay, the clay wants to stick to itself and the sand so it cannot shrink- the loss of moisture instead creating tiny pores and a lattice of strong bonds like a huge brick cube. During firing, the clay is welded/“brazed” to each particle so you get enormous compressive strength.

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green_print_business t1_jb3z10p wrote

Because sand particles are larger and more rigid than clay particles. Sand helps to create gaps or voids between the clay particles, which act as channels for the water to escape as it dries. This allows the clay to shrink more evenly, which reduces the possibility of cracking.

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xxDankerstein t1_jb5fer2 wrote

The simple is answer is: sand big, clay small. Clay particles are tiny, so they hold more water between them (more surface area per volume). Sand is basically tiny rocks, which themselves don't shrink at all. The shrinkage happens when the water between the particles evaporates. The sand is holding less water, thus less shrinkage.

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gammapsi05 t1_jb75lqc wrote

The sand keeps the clay from shrinking as it dries because the sand particles act as a filler, providing spaces for moisture to escape and preventing the clay particles from packing too closely together as they dry.

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