Typically, the glass looks better if the light source is set behind it (we light the background, not the object itself). When you choose a colored background, placing light sources becomes more complicated. Lighting of colored background doesn’t give such result as when we light the white one, especially when your background should be completely black.
Shooting glass objects on the white backgroundAs an example, we may use a bottle and a glass of martini. The scheme lighting, used by the photographer, is quite simple. Here we see a lightbox and four light sources - one on each side. The fifth source is not visible - it is installed on the floor in front, to highlight the label on the bottle.
Soft-boxes are used as modifiers, because standard reflectors make spots of light on the lightbox, whereas we need more uniform light distribution. It is necessary to light the background brighter than the object. This is a general rule for all translucent objects - we highlight the background, but not the subject. That’s why softboxes are turned around a little to the back of the cube.
When we put the items into the Lightbox, we see that the glass is almost invisible – this is not what we expect to see on the photo. So we must control the thickness of darkening the edges by using broad black screens and changing their location. That’s how we can highlight the contours of glass objects by darkening them.
Shooting glass objects on color backgroundsLet’s take a black background as an example, because black and white colors of backgrounds are widely used for photographing glass. The photographer uses two large white diffusing panels on both sides and two strip boxes behind a diffuser panel to create a good light gradient.
But here we see the main defect - the bottle looks mat when it's actually fully transparent and glossy. This is how the diffuser works here - it creates very smooth gradient reflections on the bottle sides. Thus, for getting gloss we may use black panels as screens and make gaps between them for passing the light.
You should also note the table surface. If the surface is glossy, it will act as a mirror, reflecting the white ceiling above the table. So you can use another black screen, placing it on top of the table. The photographer uses the softbox in the front to highlight the label on the bottle and olives in a martini glass. It gives one more hotspot on the front of the bottle.
Two vertical lines on the bottle is an effect that gives a small softbox when we shoot such objects as a bottle. But we don’t want the bottle to look like a zebra. When you need to make a photo of some object with both types of surfaces - glossy and mat, you need to place the light source at an angle. Thus direct reflections from the glossy surface won’t be visible in the camera. You should also mind that fluids in glass vessels often add some not very nice hotspots, but the processing of photo can fix this minor flaw. The final result is impressive!