I put my satisfaction with watercolour painting down to its elusive quality. The merest touch of colour dropped onto a wet surface can express so much. So often it is the case of what is not painted that says what is intended and in this article I shall give you a few hints and tips that will help to explain almost nothing!

To get to grips with how to depict glass you need to note exactly what you actually see as opposed to what you think you ought to see. Because we see through glass we need to paint what is behind it and, if it is a vessel, what it contains. Glass in the form of a vessel can do all kinds of things to the above depending on its make, thickness and shape. Distortion is common together with reflections and refractions.

Additionally, glass is a hard, crisp- edged material that looks worse if painted with a woolly edge. Needless to say if one tries to depict all the aspects the image could look overloaded and unreal. The trick is to know what to put in and what to leave out, along with the illusion. Imply rather than overstate – keep it simple!

STAGE ONE This vase has a complex symmetrical shape. To achieve this, a paper cut out is needed. Fold the paper in half and draw the shape against the fold – when opened out you have your symmetrical shape. Lay this over masking tape (or Frisk Film) and cut out the shape
STAGE TWO The masking tape has been cut out and masking fluid applied. When the fluid had dried, the first layer of paint was applied
FINISHED PAINTING Czech Coloured Glass, watercolour on Saunders Waterford HP 300gsm, 13?9in (33?23cm). A second layer of colour was applied to darken and define edges. I used a sponge to lose some edges. Finally I applied a transparent shadow

Masking

First things first: Don’t put an outline around a glass object. If you look carefully you will note that the edge is sometimes not even there unless the glass is tinted. I have found the most efficient way to obtain this elusive but crisp edge is to use masking tape. If the glass is straight-sided then it is simple.

However, if the glass is curved in any way a symmetrical template has to be cut. With the sides taped off you can paint what is behind or within without worrying about the edge. At a later stage in the painting you may well need to mask out the vessel in order to paint in the background.

STAGE ONE The vase has many cyclic curves so I decided to keep the whole thing simple and use my compass brush. Shown here are the brushes I typically use for glass images, notably various flats (one stroke), a sable and a fine No. 2 sable round. The masking fluid is in one lid and some liquid soap, to protect the brush from the fluid, in another. My colours for glass are typically phthalo blue and indigo. For a green tint I use intense green (phthalo) and occasionally a touch of May green by Schmincke

Masking tape is also useful when there are reflections in the surface of the glass, which may appear as lighter vertical lines. These will need to be masked out, leaving a slot that can then be lifted. You may also note reflected highlights, which can be shown by using masking fluid at the outset.

Reflections, refraction and shadows

STAGE TWO I put in the basic colours. These were worked wet-into- wet then allowed to dry before putting in the crisp shapes. I then softened areas with my natural sponge

If the glass vessel contains water the surface of the water seen through the glass will be reflective. It will also be distorted where objects such as stalks pass through. In this instance note the relative tone of this reflection as it will be different to the glass. You may see the elliptical surface of the water but only partially – another phenomenon particular to reflective substances and materials.

Clear glass usually has quite strong tonal contrasts in its reflections. Circular vessels act like lenses that both distort and magnify contrasts. Note this especially at their bases and rims. Dark liquids in a glass or bottle reflect most strongly, quite often your own face.

FINISHED PAINTING Handblown Glass, watercolour on Saunders Waterford Not 300gsm,13?9in (33?23cm). Notice where the masking on the glass has enabled me to paint the cornflower in front – this way you don’t get any muddying of the colour. Final details included intensifying some of the tones, tinting highlights and plenty of negative painting for the flowers

Again, because of the shape of the vessel these reflections are distorted, especially at the sides. Refraction is that peculiar effect that distorts any object that passes through the surface of the water. Note that the stem appears to be separated at the water surface level.

Because clear glass has no tone or colour to indicate form it cannot theoretically cast a shadow, but anything in it will. The rim, base and sides of the glass cast a shadow because the light cannot quite pass through these greater masses. Notice how, if the light comes from behind the glass container, the base acts as a lens and produces a bright light in the middle. Any texture in the glass such as subtle ribbing will produce ribbed-type shadows. If the light comes from in front, any shadows seen through the glass are distorted at the sides.

Cut glass and coloured glass

Surface decoration on glass, whether coloured or cut, produces even further challenges for the artist. I have some cut-glass fruit bowls that are immense fun to paint but very difficult and, to add to the fun, the rims are also scalloped (page 20). To paint one I start with several dots to establish the relevant ellipses, then the high and low points of the scallops.

Following this, with intense concentration, I paint exactly what I see. Well almost. The bowl invariably contains fruit of some kind. Another piece of torturous glassware I possess is a brass-based twisted oil lamp with an engraved glass bowl, through which can be seen the glass flue. Yes, a serious piece of work especially when I put in blue– or pink- coloured paraffin and light it.

Modern glass can often have colours swirled into it. The best way to achieve this effect is to work wet-into-wet whilst still preserving a crisp edge.

If the vessel is a complicated shape a stencil cut in Frisk Film* will probably do the trick. Some glass objects have surface colouring that has been cut, engraved or etched to reveal the natural glass. Similarly, as for engraving on natural glass, you can use masking fluid to delineate the decoration; I have often used this method to illustrate my oil lamp where the orange glow of the light reveals the decoration.

Glass containing coloured liquids

Tomatoes in Cut Glass, watercolour on Saunders Waterford HP 300gsm, 9?13in (23?33cm). This multifaceted glass bowl has a scalloped edge. A series of pale grey dots positioned the various ellipses, which were then painted in using a good-quality flat sable. Even the shadow had complex issues. It was difficult to know when to stop but less is more in a situation like this. You will notice a few changes, made with the sponge, and several drawing corrections. Be brave – be ruthless when working on complex items such as this

I have already touched on coloured liquids in glass vessels. In an object such as a bottle of wine you have three factors to take into account: the label, the colour of the glass and the colour of the liquid. The colour of the glass or its contents can vary considerably according to what the glass reflects.

This is particularly noticeable if there is any candle light about. Again acute observation is the name of the game. If you don’t trust your eyes, take a photograph and look intensely at the various phenomena revealed. The brain tends to deceive, willing you to simplify and make logical. Unfortunately the truth is more complex and therefore more interesting – trust your eyes.

Glass details

Elements such as bases, stems, rims, handles or any form of excrescence added to the surface basically have crisp-edged tonal contrasts. They are not necessarily outlined but owe their look to the basic shape of these quite specific reflections. Painting glass objects is, like painting water, a peculiar challenge and one that can give a great deal of satisfaction once mastered. In a future article on buildings I will refer to glass in windows!