When I was about eight or nine years old, I sneaked into my parents bedroom and sneaked out with their camera. It was an old reverse periscope affair where you peered down into the top, through a mirror set inside at a 45-degree angle and out through a viewfinder lens to aim. I took my first picture. It was a crooked, black and white affair, part of a wall and ceiling, featuring a bookcase in our dining room. I still have it (the picture AND the bookcase). I've been taking pictures ever since. And sometimes, when I see what a mess I've made of a shot, I have the feeling I've not learned much in the last forty-five years or so.
The afternoon session of the workshop I wrote about yesterday was devoted to helping artists take better pictures of their pictures. Actually, most of the attendees were crafts people with three dimensional items, jewelry, quilts, ceramics, sculpture, etc. And painters, if you think YOU got it rough photographing your work, be glad you don't do shiny jewelry, sculpture or pots. Shooting slides of paintings is a SNAP compared to the lighting gymnastics (hey, I'm not exaggerating here a bit) that the 3-D artisans go through in order to get the perfect representation of their wares on slides. Of course even painters sometimes have some gloss to their work and have to play around with angles, lights, films, etc., but man... One guy even had a kinetic sculpture he was trying to somehow capture using slides!
The speaker for the photography session was Terry Eiler, who teaches commercial photography at Ohio University in Athens. First, some general rules which seem to apply to all aspects of photographing art. Use the slowest film possible, 25 ASA is best, 64 is okay. Ektachrome is best for paintings containing blues or greens. Kodachrome is for reds; Fuji does better with yellows; Agfa is best for browns (but is not recommended for any other colors). Be aware that each time a slide is projected, it's archival life is reduced by half. Kodachrome has an unprojected life span of 200 years. Ektachrome is something like 120 years. Fuji is as little as 40 years.
Although there was much talk and explanation as to how to shoot paintings inside using various lights and films, etc., people, it just ain't worth the bother. Shoot outside, using a slow, daylight film, usually in bright sun at a 45 degree angle to either side of the work. Arrange a black or gray background to block out extraneous material, and shoot an entire roll of film for each piece of work. That may sound wasteful (not to mention expensive), but if you "bracket" your exposures, shooting one-half f-stop above and below the "ideal" exposure, you will end up with eight to ten good slides of each painting, thus eliminating the need to have slides copied, which is usually unsatisfactory. Also, those which come out a little dark often are ideal for print reproduction while those that are shot at a half-stop above ideal often look best in a hand held viewer. Always make a note of the film type, speed, shutter speed, and aperture for each painting photographed (attach it to the back of the painting) so that if you do something very right or very wrong, you'll know WHAT you did.
Some other tips--the best time of day to shoot paintings outside is between ten a.m. and 3 p. m on a sunny day. ALWAYS use a tripod. Make sure the focus is accurate of course, but pay just as much attention to the edges of the paintings when setting up your camera, making sure they are exactly parallel to the edges of the viewfinder. If you don't want to use a dark backdrop, try opening up your garage door. Then set the painting vertically on an easel in the sun, just in front of the open space. Usually, the garage is dark enough that, using such slow film, the space around the painting will be black. If not, it might be easier (and cheaper) to block light coming into the garage than to rig up a backdrop.
As for equipment, in addition to the tripod and an SLR camera, using a cable shutter release is recommended for photographing all art, thus allowing complete freedom in choosing shutter speeds and avoiding accidental camera movement of any kind. If you should decide to shoot paintings inside, two light sources are recommended, well back from the work allowing as even a distribution of light over the surface as possible. A translucent shower curtain stretched over large canvas stretchers makes a good light diffuser. Also, make sure your lighting type (tungsten or halogen) is that which is recommended for your film type. If not, a filter will be needed. Never mix lighting types.
And one other tip I picked up, slightly afield from creating good slides; is that you can often get satisfactory results in digitizing slides for Web site usage simply by projecting them, then shooting them with a digital camera (on a tripod of course). I've not tried this yet, by the way. It was an excellent workshop, selling art in the morning, photographing in in the afternoon. And if you think selling art is a tricky, let me tell you, the picture taking, notwithstanding forty-five years of experience, is often worse.