I'm trying to sell a picture of a piece of artwork for charity, and I'd like to photograph it. It's in a glass frame with lots of glare. Any ideas of what I can to to photograph it to look the absolute best? Thanks!
When it comes to glass it's all about lighting direction.
You want to make sure that when you look at the picture through the camera neither the reflection of the lightsource or anything lit by your lightsource is visible.
Hold up, I'll draw a diagram:
Glass and other shiny objects reflect light back in one direction (like a ball bouncing off a wall). The painting, which is diffuse reflects some light this way, and reflects some light back in every direction.
In the setup above, the light from a directional source hits the glass and carries on, missing the camera, thus the glass isn't visible! The same light hits the painting and some of it does get reflected into the camera so the painting does show up.
The important thing is to use a directional source, as it's possible for light from your lightsource to bounce of a white wall, and hit the glass at an angle that does go down the lens, and this shows up as flare.
This often happens when you have a white wall behind the camera, as in the above example.
The moral of the story is to make sure you can't see the reflection of the lightsource in the glass when stood behind the camera, and try to limit what the light hits (ideally it should hit nothing but the painting). You can make any lightsource directional by placing opaque objects around it to block the light in certain directions.
The key to photographing this is about the angle of light(s) used to illuminate the surface of the art. It's all about angles and reflection and it's probably easier to illustrate this (pardon my poor Coreldraw skills).
The dotted lines connecting the camera show the angles of direct reflection, so if the lighting is inside those lines, the glare will be very evident. What you need is diffuse reflection and to get that, you need to have the light outside those lines, to one side, but preferrably both.
Sorry, the reflection lines in the far sides of the camera are a bit faint...
I happen to frequently photograph artwork, including framed and with glass.
If possible, do this in a room that has black walls and no windows. If such room is not accesible, wich is my case, I use a black backdrop BEHIND the camera. This helps a lot against unwanted reflections. Also, as the other answers point out, place the lights a 45 degree or more relative to the line from the lens to the center of the artwork. It means, 2 simetrical lamps, one at each side and at the same distance from the front and from the sides of the artwork.
For example, if dealing with a 1 meter wide painting, lamps would be rougly 1 meter in front of the painting and 1 meter away from the edge of the painting. Lamp heads would be at the height of the horizontal centerline of the piece. Partly close the barn doors to limit light output so it falls only on the painting.
I Use a tripod and fire the camera using a computer and a usb cable. This is to avoid unwanted movement of the camera and to avoid my own reflection on the glass. If necesary, cover the camera or tripod's shiny spots with something matt black. (a cloth may be enough). Also remove/cover any shiny objects in front of the artwork. If the computer or remote shutter is not available use the temporizer. If that is not available either, then wear dull, black clothing, including a skull cap or simlar and keep the face behind the camera.
When framing, the lens axis should point perdendicular to the center of the artwork (specially if it's rectangular) to avoid perspective distortion. (It's correctable in post, but preferable not having to...)
In a naturally side-lighted room (lights through windows) under a clean white ceiling, laying down the glass framed painting on the floor then used a selfie stick mounted cell phone (in my case an iPhone SE) to take a picture. Slight imperfections such as straightness can be adjusted by Aviary app (free from Apple store).
I shoot in direct sunlight preferably around noon. This eliminates all glare. There may be shadows along the edges from the frame. That's why it's best when the sun is directly overhead
I used Rob's method of shooting in direct sunlight, though I did not have a frame on the artwork. This enabled me to shoot in the morning instead of at noon, and I just laid the piece on the driveway. The colors came out very well, and the only glare was on the very left edge of the piece, and it is barely visible (well, the style of the painting helps also). The piece is an acrylic pour with two coats of resin applied - very shiny!
After taking the photo I used Microsoft Image Composer to trim and apply a bi-linear warp to square it back up. I did not use a tripod, but this photo is just for posting on Facebook. I would use one if I needed better quality. ISO 400, F16, 1/200 sec (Aperture Priority) with a Canon 7D.
Use two studio strobes or floods, one on each side of the camera at approximately 45° angle to the artwork on a matte black wall, Polarize the light from your Light source with polarizing Gel filters clamped in front of the light right up against of light hood so that all the light emitted passes through the filters. Both filters will have to be oriented in the same direction. Use a polarizing filter on your lens.
Turned out all the ambient light that is not your light source. Use the modeling lights on your strobes to set your on-camera polarizing filter to eliminate all glare from the glass and the oil paint on the canvas. Keep the room lights off and shoot, bracket if using film. Polarizing Gel filters are 12" x 12" possibly larger, and have a Matt or card stock frame. you can buy polarizing gel sheets by the foot.