How does a glass scraper work?

[Jamie Buxton]

You can make a scraper with glass. Start with a piece of window glass, or an old Coke bottle, or whatever. Break it. The broken edge serves as a serviceable scraper. It doesn't have a nice straight edge like a card scraper, but it does make shavings. My question is "How does it do that?" A standard steel scraper has a cutting edge (the burr) which you're driving into the wood. All our cutting tools -- planes, chisels, knives, and such -- have a cutting edge. As far as I can tell, the glass scraper does not have a cutting edge. It does have a very sharp edge, but it is being dragged backwards across the wood, not being driven into it.

[Dan Moening]

A thermos keeps hot things hot, and cold things cold.

But how does it know which to do?

:D

Back in the days when I was a kid and could actually get ahold of a shard of glass I probably "scraped" some wood. I don't recall what the outcome was other than "wow, its smooth".

I suspect that glass as a scraper isn't producing the neat little curls that you can get from a properly tuned card scraper; but, rather, well, dust. I'm sure it will effectively sheer the wood fibers and produce a nice sheen to the wood, but beyond that its just conjecture on my part.

Have you tried it?

This should be an interesting discussion.

[Bruce Branson]

I don't put a burr on my scrapers because I only use them for very light scraping.I use smooth planes to get the surface to that point.I fettle them just like any other scraper.They cut very fine shavings of wood and don't produce dust.

[Don Henthorn Smithville, TX]

In the thirties (the last century to you younger guys and gals) I refinished several pieces of fine furniture including a marble topped table with a very ornate base. I used broken glass to scrape very nook and cranie of those pieces including the base of the table. Took a long time and then I followed up with garnet sandpaper which was all we had then. Got everything smooth, did a little staining and then applied real varnish to all pieces. They really came out well. 70 years later I have the table in my living room and it still looks good. It is a little wobbly because the hide glue has crystalized and needs replacing. Glass can be incredibly sharp and lasts surprisingly well. With a good box of broken glass you can always find a piece that will be exactly the right shape for the spot you need to scrape.