sanding a steel angle

The blue/black you are refering to is mill scale. Fairly nasty stuff, sometimes it just flakes off, other times it hangs on in the face of a grinder. In order to get the entire piece down to shiny steel, you will need a power sander. You can use a flap wheel in a high speed drill or a 4" sanding disk mounted in an angle grinder.
To get a pure matte finish you need to have it sandblasted. A small local shop might do them for you for $25 or a case of beer.
Keep in mind that as soon as you get down down bare metal they will RUST. For furniture you can spray with a clear laquer or Krylon spray but any chips will RUST. Commercial products tend to have some sort of plating: zinc, chrome, etc.
kenny wrote:

thanks! if anyone has any additional tips, they are most appreciated.
RoyJ wrote:

Best method is acid dipping. Get a gallon or two of muriatic acid at Home Depot and use a baby's swimming pool or other large plastic tub. Also buy a large box of baking soda (don't know if HD carries this but your supermarket will.) Put in enough water to cover your steel adequately, and then put on a face shield and rubber gloves and slowly pour the contents of one gallon jug into the water. Cover it with old plywood to keep the kids & animals out, and leave it overnight. In the morning take an old pair of pliers or long tongs if you have 'em, again put on the face shield & rubber gloves, and lay out a piece of old plywood next to your acid tank. Then get the garden hose running and take one piece at a time out of the dip and stand it up on the old plywood and wash it thoroughly with the garden hose. Wear old clothes you don't mind getting a few holes in. Then, when you're done with the acid dip, slowly stir in the entire contents of the baking soda box. Hopefully by the end of the box it will stop foaming. If you have a pH meter for testing garden soil you can precisely neutralize it. You can also use lye to neutralize if you know what you're doing and have some to get rid of. The neutralized dip, now a solution of ferric chloride, salt, and some complex chloride, can just go a bucket at a time into your shop sink and into the sewer system. It's not a good idea to dump it into the street drains unless they also go through a wastewater treatment plant.
Or you can just take them to be "pickled and oiled" for a few bucks, or pay huge dough to have them sandblasted.
GWE

Or my favorite: a flap disc in an angle grinder. It's much easier to get a smooth finish with a flap disc than with a sanding disc, IMO, and it handles curved areas better as well.
Depending on how tenacious the scale is, you may be able to knock it off with a wire brush in an angle grinder, which has the advantage of not leaving sanding marks. (If you take this approach, be sure to wear a full face shield with safety glasses, gloves, and a heavy shirt. Otherwise you will become a human pin cushion from the wires thrown off of the brush. They have enough velocity to penetrate exposed skin.)
Or check with a local steel supplier to see if they carry the angle you want in a "pickled and oiled" or "cold rolled" variety. Those already have the scale removed.
You can also get a pretty close approximation to a matte finish with a random orbit sander, going up to maybe a 220 grit. This will give you a slightly different look than a sand-blasted finish, but the light-scattering properties are similar.

First of all, get cold formed ones. The hot formed (black) ones are a maior PITA to get them shiny. Second, it you want to have it look like sanded in one direction, think about it another time. It is a lot of work, especially in the corners. If you want it sanded and a bit funky (irregular), do it with a flap wheel, that's much quicker. Be prepared to spend hours with that job. Best is to have a stationary belt sander, sand the tubes, _then_ weld them and go over the welds. Use anti splatter spray while welding to reduce cleanup work.
Nick

How about one of those long, thin tubs made for wallpaper? If you can find one long enough, you won't need as much acid, and it'll be easier to clean up afterwards.

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For a one time use (with a lot of care) you can use a cardboard box. Line it with one of the cheap plastic dropcloths and soak away. You can even cut and tape the box to size.
Unka George (George McDuffee)
...and at the end of the fight is a tombstone white with the name of the late deceased, and the epitaph drear: ?A Fool lies here, who tried to hustle the East.?
Rudyard Kipling The Naulahka, ch. 5, heading (1892).