Frank,

Thanks for your advice. From your post it seems like you wouldn't
expect me to have to sharpen my plane more than once per board. In
reality I find that I have to do it at least twice per surface.

At the start I thought this was quite normal because of all the grit
embedded in the wood. Now that I am down to clean wood I wonder if it
could be because of the wood itself. In certain parts it has brown
'crystal' veins through it.

Is that the silica I keep on hearing about, the great blade unsharpener?

Regards

Emiliano