Thread: Is a Coticule base slate or belgin blue water stone

Is a coticules base always slate or belgian blue coticule
and more importantly how does someone tell the difference?
Does it matter?

I ask because on another thread there was a wonderful
set of pix of a stone and the dark side looked a lot like slate
to me but I only own a stone with a slate base as
a reference and pictures as good as these were do not tell
the full story.

It can be either. Obviously, the coticules with a BBW on the other side are generally more expensive. You can also get natural combination stones and two stones that have been bonded together.

I´m not sure if I get the question.

Coticules are being sold with a backup for stability.
Nowadays most coticules come with a slate backing.

Vintages ofte came with blue belgians because they thought these were useless.

Sometimes you can still by "natural combos" with both stones naturally grown together and both sides usable and of good quality.


There is no difference in between the first two.
The backing is not meant for honing, so it is of bad quality.
Both the slate and the belgian blue used for backup often have impurities because they are not being selected

But sometimes you get lucky and can use BOTH backings.
I do have a vintage coticule with a belgian blue backside.
It has obviously not been meant for sharpening purpose.
It has a distinct purple colour. The slurry it produces while lapping is purple, too.
This is beacuase of the iron oxide content of the belgian blue layer.
I lapped the surface and managed to find a quite homogenous layer of belgian blue
that can actually be used for honing. So it is a combo hone,
even though I think it´s not natural, but glued.

I bought a "new" coticule with a slate backing, too.
The slate is dark grey with shades of black. The slurry it creates when lapped is grey.
It is a typical slate, very slow cutting in the range of 6k.
I don´t use it very often because it obviously is not meant for this purpose
and doesn´t help much.

Thanks... Hmm, my stone is old enough that it might hold a bonus.
All these years I considered the base to be just that -- a base.
This might explain why my "slate side" looks like the BBW in another thread.
Perhaps it is worth a test run on a small carbon steel kitchen knife I have.

a sharpening test won´t tell you much. Make a picture and show it to us.
Lap the surface and look at the colour of the slurry, this should indicate what it is. If it´s a BBW it must be purple.
Put the slurry on a white sheet of paper towel,
this is the best to see the colour

Originally Posted by Lesslemming

a sharpening test won´t tell you much. Make a picture and show it to us.
Lap the surface and look at the colour of the slurry, this should indicate what it is. If it´s a BBW it must be purple.
Put the slurry on a white sheet of paper towel,
this is the best to see the colour

First a picture of the stone.
The rubbing stone is much newer....

Originally Posted by Lesslemming

a sharpening test won´t tell you much. Make a picture and show it to us.
Lap the surface and look at the colour of the slurry, this should indicate what it is. If it´s a BBW it must be purple.
Put the slurry on a white sheet of paper towel,
this is the best to see the colour

Here is a pix showing the slurry from the base.
I used a small white ceramic stone to rub it as
the rubbing stone is much newer and would not
tell me which stone generated the slurry color.

The background is a neutral gray card for reference.
The color on the white ceramic and paper is nearly true. I
see that I got a bit of red reflection from the box
so the middle of the stone is not quite true.

Since I have never seen a BBW purple myself but
the slurry in daylight does clearly have a purple cast.
This is clear when compared to the photographic
gray reference card.

The stone is 5"x2.5" (12.7cm X 6.35cm).

I do have one more image that shows the texture of
the base side of my stone slightly better.

Here it is:


My goal is to learn how to tell the various products apart
as the price difference on some place like FleaBay can
be large and dark stone is dark stone.

Here's a link to some pictures of a combination.

Looks like BBW to me, nifty.

Rest assured. That's a Belgian Blue Whetstone. Not slate.

kind regards,
Bart.