Thread: is clay abbrasive?

i'm thinking of the clay you'd use to do pottery. is this stuff abbrasive? if so, what might you approximate the grit to be. does anyone know what they use as a binder in waterstones? some of the shaptons stones are described as stones fired to a high temperature with a mixture of abrasive and a clay binder. could this clay they mention be similar to the clay i'm thinking of?

Clay has many meanings. Strictly speaking clay is made up of particales of mostly silt and is usually very high in alumina which is aluminum oxide which is very hard and an excellent abrasive. Many of the Japanese finishing stones are clay based.

The grit would depend on the size of the particales. You can buy levigated alumina in all kinds of grit sizes. There is no one size. Some one else will have to answer the rest of your questions.

interesting stuff. I'm particularly looking into what could be used as an effective abrassiveless binder. perhaps epoxy? after all there are resin-bonded stones.

Clay is used in some shaving soap/cream formulas.. Had it been very abrasive, it would have had a negative effect on my blades, which it doesn't. I guess it depends on the deposit.

It depends on the partical size as well as the makeup. Some of the stuff they is more like a bentonite which has many industrial uses also.

Clay is derived from the mineral feldspar when granite is weathered and the little pieces get washed down to the ocean where they build up as layers of clay. Feldspar is hardness 4 on the Mohs Scale and steel is 5 - 5.5. The chemical formula for Feldspar is KALSi3O8 or a potassium aluminosilicate (the numbers should be subset). Clay won't abrade steel in its natural state. If you fire the clay into pottery however, everything changes because you have taken the soft sedimentary clay and reproduced the igneous process. Try taking a dull kitchen knife to the edge of a clay flower pot and you'll see the fired clay will brighten the edge.

The making of stones you're describing is called "vitrification" and the process is far from simple. Norton (now St. Gobain) has decades of experience doing it and they produce quality stones. Contrast that against the cheap Chinese stones that are on the market for a couple of dollars. They're warped, far from flat, and lack quality.

I, and other knifemakers, use the Chinese stones by soaking them in water for a few minutes and then clamping them in a vise and then forming the blade bevel. It's work but it's a welcome alternative to a noisy 1hp 2"x72" belt sander (mine is a Wilton Square D). It's fun to do from time to time. This process was shown to me in a class given by reknowned bladesmith, J.D. Smith who is known for his beautiful and tasteful damascus blades and swords.

So to sum up, clay is sometimes an abrasive but the binder use of it is inconsequential as an abrasive against the abrasive material that is held together by the fired clay.

Hope that helps answer your questions.

Well, thats not completely true. There are actually about 30 different types of clay's and they are divided up into several groups depending on the chemical makeup and physical properties. What they all have in common is they contain aluminum and silica but they can have a variety of other minerals like sodium, calcium, water and many other exotic minerals.Also clays are found in a specific subdivision in the silicate family called phylosilicates. Clay can be formed from granite but its mostly the mica in the granite that weathers away first and forms clay. The affinity for water also determines where in the scheme of things it falls. So depending on the chemical makeup of the clay the hardness can vary considerably. Also consider that few clays are pure but are mixtures of many different kinds. The micron size of the particales will determine whether its considered clay or siltstone or mudstone. Clear as mud?

Originally Posted by thebigspendur

Clear as mud?

Perfectly!

think i'll just play around with different stuff until i find what i'm looking for

new idea!

i was reading an article in the popular mechanics shop notes titled "How to make sharpening hones"

it was a simple enough. You mix cement and abrasive particles. By playing with the proportions of the ingredients and the type of abrasive, it was said you could make any grit sharpening hone.

The only trick you need to master it is to make sure the particale size in microns is well sorted. If you have exceeded your target grit with a small percentage of particales your hone will not function the way you want. Thats the art and science behind it all. You can have grit sizes smaller than your target but none bigger.

Its one of the reasons Amplex Diamond paste is more expensive than others. If you examined the stuff under high pwer mag you would see the diamond xtls are very uniform with none exceeding the grit size. Cheaper brands will not have that good a sorting. The same with a ceramic hone. I would think making one yourself would be very difficult.