For many years I offered French polish as an option on soundboards because of the widespread opinion among guitarists that  this finish is the most excellent in terms of guitar sound.  That benefit is normally attributed to the thinness of the finish.

I also saw over many years how vulnerable French polish is to wear and deterioration from moisture and chemicals, so I began trying to come up with a substitute that had the thinness of French polish but improved durability.  The solution I finally settled on uses padded varnish over a French polish substrate.

The varnish I use is readily available as Minwax Wipe-On Poly Clear Satin at Home Depot and other stores.  My process for creating a satin varnish finish on a soundboard goes like this—

• One coat of French polish applied to achieve a smooth surface, wipe off excess oil with naphtha and dry overnight.  This French polish coat serves as an impervious substrate for the varnish.
• The next morning scuff the surface with 0000 steel wool for adhesion and pad on a coat of varnish with sufficient quantity to get a wet, level surface.  Getting this just right is tricky and takes some experience.  Dry for 24 hours keeping the soundboard surface level until the varnish has become tacky.
• The third morning level any large dust motes carefully with the corner of a scraper, wet-sand the surface lightly with 2400g MicroMesh to level small motes and apply a second coat of padded varnish.  Applying this second coat is even more demanding than the first; it may take 2-3 attempts, wiping the wet varnish back off between attempts, to get a result that’s optimally free of motes.  Dry for 48 hours.
• After complete drying wet-sand the finished surface VERY lightly with MicroMesh 3600g-12000g just enough to knock the tops of f the dust motes and give the surface a smooth feel but not enough to disturb the satin texture.

Why satin varnish instead of gloss?  First of all, varnish, because of its high abrasion resistance, will hold a satin finish much better than satin lacquer, which self-polishes quickly to gloss just from contact with hands and clothing.  The satin texture of the varnish also has a couple of visual advantages: it produces less glare which can be kinder to the eyes of audience members in a recital situation; it disguises tiny defects in the finish surface which are an unavoidable part of this finishing strategy.

My satin varnish finish is about as close as one can get to an ideal substitute for French polish.