Most of the posts in various online forums recommend taking the photos outside. Some people say direct sunlight is best; others say that the sun washes out colors, and that you have to find a shady spot outside.
Time and Weather Conditions
I took these photos at 2:15pm, when the sun was still high but at a good angle for me to take direct overhead shots without getting shadows. It was a clear day with a few wispy cirrus clouds high up in the distance, and none directly overhead.
Option 1: Direct Sunlight
Here is the best photo that I got outside in direct sunlight. With the sun coming at somewhat of an angle, the painting seemed less washed out than if I had taken this at noon.
ISO 100 ("Low" setting), 1/125 sec at f/11.
It's pretty green-toned, which is similar to the original. However, the colors are washed out in a way that I don't like. In the original, the gradations of the washes are much more noticeable. The sunlight washes out the crispness of the colors.
Editing the photo resulted in this.
Pumping up the whites and highlights resulted in almost losing the subtle colors of the beak, the neck, and the tail.
Option 2: Full Shade
Now here is the best photo that I got outside in the shade. I took this photo in the shade of a large tree. The tree was to the west-northwest (WNW) of me.
ISO 100, 1/125 sec at f/3.5.
In the shade, I had to increase the aperture from f/11 to f/3.5 because it was so much darker than before in the sunlight.
I don't like the bluish tint. The original painting has no blue in it, not even in the shadow. The shadow here is very blue and violet.
Adjusting the photo's temperature and tint weren't enough to get rid of the blueness. However, I was able to remove the blue cast by choosing Blue under Color in Lightroom, and then setting Saturation to -100 and Luminance to -60.
Despite the awful bluish tint, the colors do seem a little less flat. There's a little more variation to work with.
Editing this photo resulted in this.
Note the nice darkness of the beak, neck, and tail, which I couldn't get in the direct sunlight version. Also note the slightly bluish shadow. It's not supposed to be bluish, but I couldn't fix that any further.
Finally, note how the paper color isn't as white as I'd like. I tried to increase the whites to fix that, but that resulted in losing too much color from the beak, neck, and tail.
I'm not sure, to be honest. When I first performed the experiment, I thought shade won over direct sunlight by a small margin, because the colors were less washed out and seemed to give me a wider range to work with. However, looking back at the original photos and final edits a couple of days later, I prefer the sunlit version.
In the future, it would be interesting to see if overcast skies improve the tint and range. My guess is that you get the best of both worlds, since the clouds would act as giant reflector-diffusers in the sky and balance the light out.
I would also like to know if taking photos of watercolor paintings indoors with studio lighting solves the problems that I had.