Using Marble as a finishing stone

[Johntoad57]

Today I was talking to someone who told me he used a small marble slab as a finishing stone for his straight razors. He said it was 3" X5" and was polished on one side. He also stated that it gave him really smooth edges on his razors. He seemed to be genuine (he knew a lot about finishing stones), but I have not heard anyone mention marble here on the forum. I'm still relatively green when it comes to finishing stones so I couldn't say. Is Marble a good medium to use as a finisher?

[DoughBoy68]

First off, Thank You for your service!

Have not heard of using marble but it doesn't mean it hasn't been tried. I have thought about it a time or two in the past but never got past the thinking stage. Would also like to hear others thoughts and experiences with marble.

[RayClem]

Marble is primarily a compacted form of calcite the mineral formed by the sedimentation of calcium carbonate. On the Mohs scale, which classified minerals by hardness (the ability to scratch minerals lower on the scale), calcite is rates as a level 3. That is pretty soft.

A knife blade or razor would rank somewhere around 5-6 on that scale depending on the degree of hardening. For comparison, your teeth are composed of a mineral called apatite (primarily Calcium phosphate with some trace elements) are around 5 on the scale. That is why your dentist can use a stainless steel dental pick to scale your teeth without scratching the enamel.

Most of hones are comprised of harder minerals such as Orthoclasse Feldspar (Potassium Aluminum silicate- 6 on the scale), Garnet and quartz/silica are about 7 on the scale, Beryl/Emerald (about 7.5 on the scale, Topaz/Aluminum silicate (8 on the scale), Corundum/Ruby/Sapphire/Aluminum oxide (9 on the scale). Even harder minerals are silicon carbide and cubic boron nitride which fall between 9 and 10 on the scale. Diamond, which is the hardest mineral known to man is ranked 10.

Thus, stropping on marble might help straighten the edge of a razor, just as linen and leather can do, but it it is not hard enough to hone the edge of the razor.

[PaulFLUS]

I too have thought about using granite, not marble because I know marble is soft. You can scratch it fairly easily with a screwdriver, and yes I found that out the hard way. Granite comes in somewhere between 6 and 7 depending on the formulation so I would think it would be fairly good as a finisher especially if it is very very smooth. I have a granite table in my breakfast nook I have been meaning to try but have just never done it. The wife would probably kill me if I did. I would also imagine quartz is fairly good as a finisher since it is the primary component in granite.

[Gasman]

I dont know enough that i could argue with Ray, so i will just say thanks for the mineral lesson Ray. That was a lot of big words for me.

[thebigspendur]

Granite is composed (usually) of three things: Quartz, Feldspar and Mica. The hardness of the three vary tremendously and the distribution of these minerals is totally chaotic. So, if you used a granite hone you blade would be simultaneously exposed to all three.

It doesn't sound like a good idea to me.

[Johntoad57]

I'm hoping Glen or Mike (gssixgun or Outback) will chime in here and give us the definitive answer. I consider them the resident experts when it comes to honing!

[bouschie]

Never used marble. Think it is too soft. I have used 1/2" thick glass and Theirs Issard strop paste. Worked very well for me.

[outback]

Well I'm no pro..but I'd have to agree that both would be of no good. For all the same reasons, the make up/ composition of each are too wild.

Or in layman's terms.

You'd be honing on a complete progression of naturals, with each pass.

[Johntoad57]

And there you have it! No BS or long winded geological analysis, just a nice clean answer that is straight up.

Thank You Mike!