It’s possible to decrease it. Take the photo, then turn the painting 45 degrees. Don’t move the lights. Just turn the painting on its side. Take another photo. Turn the painting 45 degrees again (so now it’s upside-down) and take another photo. Do this again so you end up with four photos, all having glare on them IN A DIFFERENT PLACE from the same lights/windows/whatever.

In Photoshop, choose Panorama and merge the four photos. The glare will be pretty much gone. I have done this when I got glare from glossy paint or when I forgot to take a good photo before I varnished. It works.

Harold Roth is a genius! I’m going to try that too! I’m certainly no photographer so Ive always blamed by poor photography skills. but this might just work!
Thanks!

Must try the Panorama in Photoshop!

Some years ago I found in https://www.aucklandartgallery.com a text in pdf, “Standard Copying Technique” with a chapter called “Eliminating surface reflections with a digital camera”. The pdf is not available online now. Anyway, the text is:

“When physical constraints prevent you from positioning your lights optimally, or when you cannot or don’t wish to use polarising filters you can remove the reflections with your picture editing software.

This technique can be used to photograph textured glossy surfaces, (not just paintings) and through glass.

It does not produce the contrast increase obtained by cross polarising using film.

This is an ideal way to photograph miniatures mounted behind curved glass.

The technique consists of shooting two separate images, and using only the best elements of each image.

Photograph the subject once with a light on the left hand side, and once with the light on the right hand side. The subject and the camera must not move between exposures.

Superimpose the two images as layers or objects in your picture editing software. Choose Darker or Merge if Darker.

If the two images did not contain overlapping reflections then all the unwanted highlights will be removed.”

Hope it helps.
Jose