It's occasionally mentioned here and elsewhere that various meshes, steel wools, botanical reeds, wooden paddles, sweepings from covered bridges...and brown paper bags are 'grits' equal to specific sanding grits.
Are these equivalents determined by comparing abrasive effects, microscopy, or what? Are the grits the same for each material and the equivalents reasonably precise or do they vary widely according to which 'web authority' says so, which grocery store we prefer, and which way we use the bags?
Given that grits on sandpaper and sharpening stones have at least 2 or 3 different systems, starting from there leaves a lot of room for misconstrusion, especially if your "web authority" does not specify exactly which grit system they are comparing stuff to...much less what basis of comparison they are using - they may not know, if their basis of authority is some magazine article which they dare not mention since they are pretending to be an authority, when they are actually just parroting, and the magazine article may itself be parroting some other source. A lot of that goes on, and myths as well as misconceptions get continued that way.
Steel wools might be somewhat consistent, but reeds, paddles, covered-bridge sweepings and brown paper bags are all likely to vary due to differences in base material and specifics of construction/growth/manufacture. Ferinstance, there is locally a clear difference in texture (to the fingertip) between the brown bags at the grocery store and the brown bags at the liquor store. Certainly I'd expect quite a difference between basswood and teak for the wooden paddle or handful of shavings, given both a difference in hardness and a silica component in the teak. But I mostly just use sandpaper and Beall buffs on bowls, and sandpaper and old rags on spindles. Whatever works and makes you happy...
Early in my turning years, a guy told me the 2000 grit line. I used it to burnish Christmas ornaments. I got over it.
Grocery bags have two problems: 1 - they don't grade the grit to any standard I know. I doubt if the paper mills share their brown bag recipes with each other to gain consistency. 2 - The grit of any one bag is probably quite variable from the coarsest to the finest grits. I pay good money to know that my 1000P paper is within +/- a few gritss of that size.
Don't try the white plastic ones either - makes a melted globby mess all over yer just finished blackwood vase - not to mention the pain of liquid plastic on yer digits.
I've also noticed the difference in bags, some seem to be "slick" feeling... and don't seem to be as absorbent as the "normal grocery bags that I store blanks in..
Anyone stationed in or who visited Germany in the 60's might remember their toilet paper. I think it was about 100 grit equivalent. You didn't use or need many swipes to get the job done! I think it was strong enough to get the better of some wood.
: Then there was the British toilet paper of the same era: Super Glossy!
In the current Harper's Magazine, there's a really amusing series of quoted letters between various peo\ple in the British health beurocracy, concerning the toilet paper issue. Apparently the super glossy stuff (which wasn't absorpent) was chosen deliberately. I always though it was cheapness, but that ain't it.
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