I had a chance a couple weeks ago to take proper photos of my newest paintings, and I thought I would show the great setup we use. My pal, Scott has researched and become a proficient photographer in the last couple years, and he has a great method for photographing artwork that gives you no glare.
"Polarizer gels are used on flashes in conjunction with a polarizer (linear or circular) on your lens to decrease specular highlights. This is primarily used when you want to photograph flat artwork. The most common setup involves 2 flashes positioned 45 degrees (relative to artwork surface) on equal distances from either side of the piece. Each flash (light) has a polarizer gel on it aligned in the same direction. The polarizer on the lens of the camera is aligned so it's axis of polarization is perpendicular to the polarizer axis on the flashes. This will eliminate unwanted specular highlights in the artwork."
In the below photo we are using 4 lights, but the more common (and affordable) setup would have 2.
Another tool that can be used is to photograph a printed color matching card with the painting to use to color correct in photoshop. Looking at some pure color boxes, just tweak the photo to match the sheet rather then trying to judge shifts in your more complex artwork.
Below are photos take seconds apart in the exact same lighting conditions as shown above. One quarter turn of your camera's polarizing lens filter makes the difference below.
Similar lights I'm about to buy for reference photography and photographing artwork:
Polarizing film available at: