Today I did a quick demonstration, including some tips on how to paint clear glass. Following are 5 steps in the process, about an hour total painting time. I don't necessarily consider this a finished painting, but for today's lesson, it is done "enough".
Step 1. Block in
Some artists will do a complete painting at this step, in monochrome (only one color). They will resolve all the problems of the painting except for color. And then, after this dries, they will begin adding in color, sometimes in transparent glazes, and sometimes with opaque paint. I chose to just use this stage as a "block in" to get everything in place.
tip: use a lead primed surface or an oil primed panel. Regular acrylic gesso will not allow you to wipe off the lights as in this example.
2. Adding Background
Here, I have laid down a basic background color. Notice that I have just painted the background over the wine glass, except for where the wine is. Glass is transparent, so the background color must show through. Rather than try to paint around the edges of the glass, which might leave little ridges of paint, it is much better to just paint the background behind the glass, and then go back in to indicate the shape later. Someone once told me "Never let your background know what your foreground is doing". In other words, try never to paint around objects with your background color - it is better to paint into the edges of something, and then go back and establish the edges.
tip: Keep shadows warm in color. Remember the rule: Cool light, warm shadows. Unless your still life is sitting in a sunny window, you will probably have best results using cool light.
3. Adding More Color
At this point, all I am doing is simply adding "local color" of the objects. The basic darks of shadows and lighter areas, that's it. No detail. Now that I have most of the panel covered, I can start to delineate shapes.
tip: Try to go for the "big picture" with shadow and light patterns. Get the basic form before you start adding detail. As fabulous painter Don Hatfield says, "The forest before the trees,the dog before the fleas."
Step 4: Painting the glass and adding some detail.
Glass is really quite easy if you understand two basic rules. Rule #1 is that because it is transparent (or, in the case of some colored glass, transluscent) light passes THROUGH it. That means that light will hit the glass, and travel to the other side, where it is refracted. The effect of this is that the side AWAY FROM THE LIGHT will actually be LIGHTER than the side where the light is coming from. This is sort of against our usual way of thinking. Here are three other examples. Look at both the clear glass and the colored glass..
The left edge, where the light is originally hitting, is darker than the right side, where the light is passing through and bouncing around.
Rule #2 for glass is that catchlights occur where the form bends. So, in the example immediately above here, the catchlights hit where the neck of the bottle turns into the rounded bottom, and also at the lip where the rounded edges hit the neck. There can be all kinds of reflections too, of course, and usually one large highlight will show up at the point most directly perpendicular to the light. You have to decide when painting glass how much of these things you want to indicate.. I have downplayed some of the lights and reflections in both these paintings.
A good starting color for most clear glass is veridian, mixed with either a little black or some transparent red oxide to darken it a little. This would be the mix for the edges closest to the light source. There is unfortunately some glare on our example from today's demo, or this would show up more clearly. For the lighter side edges, a mix of veridian and white usually works pretty well. Colored glass of course will have to be shades of the local color, whatever that is.
In today's demo, I darkened the left edge and then indicated the other edge with a lighter mix of veridian and white. Glass usually works best painting wet into wet, or at least your edges should be fluid and smooth.
tip: Catchlights and highlights on glass are sharp and crisp. Use plenty of paint, put it down and leave it! No fussing!
Step 5, the finish
Maybe this shows a little more clearly. You can see that the left edge of the stem is dark,while the right edge is lighter. On the bottom of the glass, there are dark edges, and the color of that part just partakes of whatever it is near, in this case, some of the table color and a little bit of the white cloth behind it, both slightly greener because of the slightly greenish color of clear glass. The highlights fall on edges where planes turn, and I've just indicated very slightly a few reflections. By the way, wine is also transluscent, and so it will also be lighter on the side away from the light.
Otherwise, I just simplified some of the shadow shapes, and clarified a few edges. If I wanted to "finish" this, there would be another go at the background, and of course to add some detail to the table itself and a bit of refinement of the cloth.