What is a value scale and how do I actually use one?

Value means how light or dark something is, ignoring its colour. It is the property that carries almost all the information about form and light, and it is the property people are worst at judging, because the eye adapts constantly and compares whatever is next to whatever. A physical scale removes the adaptation problem: you are comparing two things that are touching.

Step by step

1. Make the scale rather than buying one.Rule nine boxes about 20mm square on a strip of the paper you actually draw on. Box 1 is untouched paper. Box 9 is the darkest your darkest pencil will go on that paper, built in several layers. Then fill 5 as a true middle, then 3 and 7, then the rest.
2. Get the steps even, not merely different.The test is that no step should jump more than any other. Look at the strip from three metres away and squint — any step that stands out has to be adjusted. Most people find the dark end bunches up, because paper stops accepting graphite before you have run out of intention.
3. Punch a hole in the centre of each patch.A hole punch, or a craft knife point, through the middle of every box. This is what makes it work — you see the subject through the hole, surrounded by the grey, and the match or mismatch is obvious. A scale without holes is a decoration.
4. Find the extremes of the subject before anything else.Hold the strip up and identify the single lightest and single darkest point in what you are looking at. Mark both on the drawing early. Everything else now has a range to sit inside, and you cannot accidentally squeeze the whole picture into the middle.
5. Reduce the subject to about four values, not nine.Nine steps is for measuring. For actually building a picture, group everything into light, mid-light, mid-dark and dark. A drawing with four clearly separated value groups reads powerfully; a drawing with nine subtly separated ones reads as grey mush.
6. Check the drawing against the scale as well as the subject.Lay the strip flat on the drawing. If the shadow you have called dark reads as a 5 rather than the 8 you measured in the subject, the fault is now measurable rather than mysterious.
7. Keep one scale per medium.A charcoal scale, a graphite scale and a watercolour scale look different, because each medium has a different darkest possible black and a different surface. Ten minutes making a scale in a new medium tells you immediately what range you are working inside.

Tips

• A greyscale photograph of the subject on your phone is a fast substitute and a good cross-check, but a phone flattens the darks and lifts the shadows, so trust the physical strip when they disagree.
• If you cannot get a convincing black, the paper is the limit rather than the pencil. Smoother papers reach a deeper black with graphite; textured papers hold more charcoal.
• Squinting compresses what you see to about four values automatically. It is a value scale you already own.
• Laminate the strip or cover it with clear tape. An unprotected one gets grubby and every reading shifts.

Common mistakes

• Making the scale with the pencil grades rather than with pressure and layers — A scale labelled HB, 2B, 4B is a pencil chart, not a value scale. Grades do not step evenly, and you can reach most of the range with any one of them.
• Skipping the holes — Without a hole you are comparing two things that are near each other rather than touching, and the eye adjusts in the gap. The hole is the entire mechanism.
• Using nine values in the finished drawing — Too many closely spaced tones destroy the reading of a picture. Measure in nine, paint in four.

Questions people ask