There is a sharpening system known as scary sharp.  It typically involves adhering sand paper down to glass plates.  Start at a high grit, and sharpen your tool down through the grits.  It is perfectly valid, and can give you a great edge.  The only issue is the cost of sandpaper adds up.

If you only have a few tools to sharpen, it works great.  Sometimes you want to clean up a really rough ebay tool, and don’t want to use a nice diamond stone on a rusty hulk.  Flattening water stones is rough work, and best done with disposable sand paper.  They can help flatten issues on cast iron tables.  Basically lots of good uses.

I have some decent diamond stones, but still wanted some glass plates to do occasional sharpening and clean up with sand paper.  I went to a local glass company and told them I wanted 1/4″ 4×10″ float glass for this purpose.  I ended up paying 50 bucks for 9 plates.  The edges are a little rough, but not sharp.  Just not pretty.  They even put nice little square foam pads as feet.

I am tickled pink at how nice and affordable these were.  I don’t plan on using them a lot, but at the price I got how could I not go for a pile?  This is probably a stash beyond life expectancy!  I would urge woodworkers and tool users that need to sharpen flat objects to go to their local glass shop and see what they can do.  A little super 77 spray adhesive to stick the paper down, and a sharpie, and you are in business.