There are strong similarities between metal and glass, though in a sense they are opposites. Both have hard, smooth and reflective surfaces, but while metal reflects all the light falling on it, glass lets most of it through.
Painting objects made of shiny metals can seem daunting at first. Instead of a solid form to grasp which obeys familiar rules of light and shade, you are suddenly plunged into an upside down world where many of the strongest tones and shapes derive from things out side the object. In the case of a very shiny object such as a stainless-steel, the form seems to be a sum of other objects, shapes and colours around it. Move it to a different place or even just shift your position slightly and you have a completely subject.
Glass is one of the simplest of textures to render as long as you understand what is going on. You will need to learn how to deal with its two main characteristics, transparency and refraction. Transparency can be a difficult concept for the painter. A common mistake made by beginners is to make the glass object more prominent and dense than it actually appears.
The edges tend to be over-emphasized and the middle transparency filled in as though trying to make the whole object into a solid form. See if you can approach the problem from the other direction by asking yourself what is the least you can do to indicate glass. A few brushstrokes are sometimes all that is required, some light ones to show the turning of the form and a couple of rapid marks for highlights.
The principle of refraction is also useful to the painter in revealing the texture of glass. Refraction is the name given to the way light rays are bent as they move through a denser medium. It is exactly the same phenomenon as you find when looking at the way a stick seems to bend in water. If you look through any glass you will see this to a greater or less extend, shapes, lines and textures of objects behind the glass will be distorted.
Experiment by placing objects behind the glass and see whether the distorted forms help show the textures of the glass. Think visually and choose objects, shapes and colours that might give an exciting image.
One of the most difficult problems for painters, no matter how good they are, is to try and make sense of a confused jumble of interminate tones. Look into the surface of most metal surfaces and that is usually what you will find. So whether you are simply drawing one object or tackling a still life which includes reflective surfaces. You will need to consider how to simplify and clarify the subject.
This can be done by paying special attention to the lighting. Remember that the slightest change in light and its intensity will alter the appearance of reflective surfaces and textures. Strong direct light will tend to give hard and vivid contrasts, while softer light will break up the tones, giving more subtle effects.
The simplest ways to experiment with different light sources is to place the objects on stray so that the composition remains undisturbed and can be transported to different locations around the house. Sometimes by changing the light the whole idea of the painting can alter.
In any still life group - and even a drawing of an isolated metal or glass object is a still life the background is of great importance and in the case of metal and glass can help you bring out the qualities of the objects. The smoothness of a copper pot or silver jug, for example, might be stressed by painting it against a rough-textured wall or a heavy fabric, while a plain, dark background would provide an element of contrast to make highlights and tonal contrasts in the subject stand out more strongly.
With glass, the background will always be a dominant element, since so much of it will be visible through the glass. Plain backgrounds are usually best as a strong pattern behind a glass object will destroy its form, but the colour and tone will depend on the effect you want to create. Some of the most successful paintings of glass have been done on dark backgrounds, which emphasize the transparency by providing a range of subtle mid-tones and brilliant highlights. A successful water colour of metal or glass should be as fresh and sharp as the forms it is describing. A water colour will record every step you make, so it is essential to paint with a clear idea of what you are doing. Mistakes cannot be easily rectified.
So before you begin, look carefully at your subject to see whether there are any small highlights you can safely leave out for example or several mid-tones you could merge into one. One of the basics of all painting, but particularly relevant in the context of water colour, is to "make less say more."
One of the most techniques for clear, sharp effects is wet on dry, which simply means laying a wash, allowing it to dry, and then laing further washes on top. Each new wash will leave a crisp, hard edge which can be very effective for subjects like cut glass or a faceted metal object.
For softer gradations of colour and tone, you can soften edges with a moist brush. Wet into wet techniques can provide interesting effects in rendering glass and you can control and soften the colours by using blotting techniques. You can also work back into the dried water colour with an opaque media such as gouacheighten tones by brushing on clean water and then blotting, or rub carefully with a soft eraser, which will remove a little colour from the surface.
As a first exercise, choose a subject that has a comparatively simple form, such as this spoon and observe how the changes in the surfaces create corresponding. This painting (the spoon) began as a water colour and as the tones built up, opaque gouche was introduced to lighten the tones and correct mistakes.