There was one time when I was tasked to photograph several portrait paintings. No, this is not like taking pictures of people or some scenes using my camera phone. Photographing a portrait painting is really serious and my client meant business!
In one of my test shoots, I noticed a bluish glare on one side of the photo I got. There can be several reasons for this.
When you think about the un-flat surfaces of the portrait panting subject, and the light from an umbrella used in the studio it seems obvious that you will really get glare or reflections. The solution: large Polar sheet filters placed over two 45 degree angled strobes with round reflectors is the answer.
It is also possible that you are getting lens flare. When this happens, check the lens of your camera, look through it, and make sure that there are no reflections in the lens.
My friends checked my set up and camera setting and suggested me these and those. It took me several test shots before I was able to completely remove the hot spots.