The Case Of The Missing Blue Stone

In this photo, you can see the small space where the blue stone belongs. When my son and I go to France this June, we'll be on the lookout.

How's this for an unspeakably beautiful oven

Here's an email I received today. If you have any information about the BLUE STONE, please get in touch with Marcus Flynn: pyromasse@gmail.com

Hello,
My name is Marcus Flynn and I am a builder of Masonry stoves, and on
occasion ovens, and I eat bread regularly.

There is an English man in Brittany who is asking me some questions
about an oven he has just aquired with a property.
In the second image of the oven detailed here
http://www.pyromasse.ca/ovensfr.html there are three large dark brick
visible at the back of the bake chambe ( which is cold )The owner told me
that these brick would change colour when the oven was at opporating
temperature. I took little notice at the time. Now though the man in
Brittany is asking me about a special stone that fits into a nich in the
ovens facing just below the avaloire, and changes colour when the oven is
hot enough ( for what ??? ) The stone has been lost but old people have told
him that it is called Pierre Bleue ( blue stone ) and that it comes from
another area of france.????

Do you know anythig about this stone ? Or do you know the supreeme
athoraty on French Ovens ? who I can ask. I have heard about it only on the
two occasions mentioned above, both of which are more or less in the same
location.