Thread: belgium blue

Unfortunately, "they" were simply going by what they see and experience. The truth of the matter is that with natural hones, it's impossible to say that a blue hone is this and a yellow hone is that... Nature made those hones, and Nature isn't big on quality control..... or carefully checking the ingredients before making honing stones. The Coticules are particularly difficult to catagorize as the garnet crystals as so different from other abrasive crystals in the way they cut and behave. However, your point that there are generally fewer crystals in the blue vs yellow is correct and I seem to recall that the crystal size might be slightly larger in the blue but again, you can't tell for sure as this can vary from sample to sample. What you are forgetting to take into account is the binder in the blue vs yellow rock. The actual sediment that binds the rock together also has a profound effect on it's honing ability even though it does not do any honing itself. Yellow coticules in particular seem to vary more than the Blue in this regard, some being soft, others hard and many more somewhere in between. Soft binders will allow a slurry to develop quicker, allows the garnets to protrude more from the substrate by wearing away quicker and allows dull garnets to be shed faster which all promotes faster honing. A harder substrate would retain the crystals, keeping the tops closer to the surface and retain them longer, allowing them to round over more before being torn loose. That would result in a slower cutting, smoother polishing hone than the first one.

Manufacturers use the same tricks when making hones and grinding wheels. The harder the steel you are trying to grind, the softer the binder in the grinding wheel, which allows the grit to shed before it dulls too far and simply creates friction that heats the steel rather than cut it. That's why machine shops use white wheels (or pink, or blue... ) to cut high speed tool steels but welding shops stick to those hard, tough grey wheels that grind soft steel just fine but need to be dressed with a diamond point to refresh the surface and remove the embedded swarf.


Regards

Christian

Well good explanation but all a bit confusing for me. how would i no my yellow is a good polishing hone i would say when i rub with slurry stone it does create a slurry but not as quick as i would of thought .

Originally Posted by gary haywood

The other thing i can't understand is they say blue is a 4k and yellow is 8k.The way i see it is there both the same except the yellow produces more garnets which makes it a faster cutter? and blue less which makes it a slower cutter so surley you could start on yellow and finish on the blue and it is the garnets that do the cutting in the slurry may be some one can explain?

Gary, the quantity of garnets is linked with the numbering 4K and 8K.

BBW: 4K grit (=4000 grit), so there are approx. 4000 garnets in one square inch BBW surface

Coticule: 8K (=8000 grit), so there are approx. 8000 garnets in one square inch Coticule surface

The more garnets there are in one square inch surface the smaller they are. So a Coticule garnet is smaller then a BBW garnet.
The smaller the garnets the faster you can sharpen your razor.

Side note --> the use of a slurry stone gives us 2 advantages: 1. it creates more slurry on the surface of your honing stone & 2. the garnets in the surface of both your honing stone and slurry stone are rubbed together. This way the garnets will be smaller then when not using a slurry stone.


@ kaptain_zero

Very nice explanation!

Thanks for that info good explanation but you'd think a 4k would cut quicker than an 8k that is the case with the norton if you need to remove more metal you'd use a lower grit and polish with higher grit. I should get my bbw tomorrow morning i will try it before my yellow and finish with yellow and see what happens.

Originally Posted by gary haywood

Thanks for that info good explanation but you'd think a 4k would cut quicker than an 8k that is the case with the norton if you need to remove more metal you'd use a lower grit and polish with higher grit. I should get my bbw tomorrow morning i will try it before my yellow and finish with yellow and see what happens.

You have to understand that there's a difference between 1. removing an amount of metal and 2. creating a sharp edge.

Case 1. : lower grit --> less garnets in 1 square inch surface --> bigger garnets because there are less garnets in the surface (15 to 20 micron for the BBW)

Case 2. : higher grit --> more garnets in 1 square inch surface --> smaller garnets (+/- 5 micron for a Coticule)

So in case 1 you can say that you are removing a lot of metal when honing your knife/razor. But removing a lot of metal isn't the same as creating a sharp edge! Because the garnets are bigger then in case 2 it's difficult to create an edge that's as sharp as in case 2.

In case 2 you can also say that you are removing a lot of metal because you have a lot more garnets (more garnets but smaller garnets) then in case 1. And because you have smaller garnets then in case 1 you can create a much sharper edge then in case 1.

I hope this clears things up for you!
If not, shoot your questions!

-Rob

Originally Posted by Bart

But either way, I'm still no big fan of designating a grit rating for natural Belgian hones. People often start believing that they can interchange the Blue/Yellow with the Norton4K/8K, while they are in fact pretty incomparable.

So true!

But at one point we need to classify them otherwise they are difficult to sell!

Originally Posted by JimmyH-AD

FWIW, the yellow side has what looks almost like a spider web of purple throughout it's surface so that may account for it's performance.

BBW stones with many of those purple particles in them perform as good as a Coticule. These purple particles contain a lot of garnets (sometimes even up to approx. 12 000 garnets!).

Originally Posted by ArdennesCoticule

BBW stones with many of those purple particles in them perform as good as a Coticule. These purple particles contain a lot of garnets (sometimes even up to approx. 12 000 garnets!).

A stone collector friend of mine says that the vintage coticules of days gone by had more garnets per square inch then the rocks that are harvested today. Would you say this is accurate ? It seems to me that the deposits are thousands of years old regardless of when they are mined. IOW, a coticule mined today is potentially as good as one mined fifty years ago ?

Rob in case two would you recomend after use with bbw finishing with a slight slurry or water on the yellow i have just purchased yellow coti from ardeenes and bbw i'm sure with use i will sus it out but i'm just trying to get all the info ican but your explanation makes sense.

For me personally, if I feel the need to do some honing on the blue, it's blue with slurry until I'm happy and then I move on to the yellow with water only. If the razor doesn't need much work but rather I'm just trying to freshen up an otherwise fine edge, I'll not bother with the blue and go straight to the yellow with water... if it seems to be taking a bit too long, I would raise a slurry on the yellow and continue using the same stone until the edge improved and then rinse the hone and go back to plain water. I would not bother using slurry on both hones if I'm using both on the same razor, so it would be like above, blue w/slurry, then Yellow, no slurry. You can of course experiment with different things yourself... after all, you are the only person in the world with those two exact hones, they might just respond differently than my two.

Christian and yes, I'm aware my name is not Rob, but I like to answer things anyway!

Originally Posted by gary haywood

Well good explanation but all a bit confusing for me. how would i no my yellow is a good polishing hone i would say when i rub with slurry stone it does create a slurry but not as quick as i would of thought .

If you want to use your Coticule as a finishing hone, than don't worry about slurry. According to a booklet, written some 30 years ago (in French) about Coticule, fast and soft coticules were used to form the edge. Next they went to a harder coticule for finishing the edge.
As long as your coticule isn't so soft that it produces slurry on it's own, your coticule will finish just fine with water only. Raising slurry is for fast steel removal. Run a perfectly honed razor for 10 laps on a coticule with slurry and test shave. You'll know instantly why it is not recommended as a finisher in that mode.
For use as a finisher, I've really never found much difference between the Coticules I've tried. The differences really emerge when you raise a slurry on them, and then we're primarily taking about speed of steel removal.

Hey Rob, I was unaware that the Belgian hones contain 4000 and 8000 garnets per square inch.
Thanks for sharing that.
But either way, I'm still no big fan of designating a grit rating for natural Belgian hones. People often start believing that they can interchange the Blue/Yellow with the Norton4K/8K, while they are in fact pretty incomparable.