Weathed open grain wood

I'm sure I recall seeing something on here about a product that could be painted onto old weathered wood that penetrated and filled where the grain had opened up but I can't remember what it was called - and maybe even remembering wrong.

I looked at a job yesterday with three doorsteps that are sound but very much opening up. He did want them stained but I think by the the time the splits are filled it will look awful and probably needs painting instead.

Anyway does anyone know about the...

Weathed open grain wood