The Grid Method in Watercolour and Charcoal

A pencil grid under watercolour works only if you get it off the paper before you paint, and a charcoal grid works only if you draw it in the medium itself and keep it coarse. Two media, two opposite disciplines, one method underneath.

So the whole method comes down to a sequence: grid the reference, transfer the drawing lightly, erase the grid completely, then paint. The first half of this article covers each of those, plus which pencil to use (it is not the one most grid tutorials recommend) and what to do when a line does survive into the finished piece. The second half turns to charcoal, where the grid is drawn in the medium itself and the question is not how to erase it but how coarse to make it and when to fix it.

Watercolour: Erase the Grid Before You Paint

What You Need

Paper

Weight. 140 lb (300 gsm) is the standard working weight and the one to buy, but it does not stay flat on its own: it cockles under a wet wash, which is why the stretching step below exists. 300 lb (640 gsm) stays flat without stretching and costs roughly twice as much. Anything under 140 lb cockles badly enough that a grid drawn on it stops being square once it is wet.

Surface. Graphite settles into the valleys of cold press texture, so clearing a line completely is harder there: the eraser reaches the peaks long before the hollows. On hot press the lines sit on top and lift cleanly, which makes it the easier sheet to grid and suits the crispness of botanical work. The trade is that washes dry faster on hot press and are less forgiving, so a wet edge left standing becomes a hard line.

Sizing. Watercolour paper is treated with gelatine or a synthetic size so paint sits partly on the surface instead of sinking in like blotting paper. A sheet sized both internally and externally takes masking fluid and survives lifting. A lightly sized sheet drinks the paint on contact, which makes corrections close to impossible.

Stretching. Stretch the paper first, grid it afterwards. The sheet expands while wet and does not return to the same dimensions, so a grid drawn before stretching comes back distorted. Tape all four edges with gummed tape and let it dry fully.

Pencil and Eraser

Use an HB, and hold it lightly. Most grid tutorials, including the ones on this site for graphite and charcoal, recommend a 2H, because on drawing paper a hard pencil stays pale and lifts cleanly. Watercolour paper is different. A hard point presses a groove into a soft, absorbent sheet, and when the wash arrives the pigment runs into that groove and dries as a line darker than the pencil mark ever was. Erasing does not help: the graphite comes off, the groove stays, and the groove is what you are seeing. HB gives you a visible line at a pressure light enough not to emboss. Anything softer smudges into the wash and greys the colour above it.

• Draw from the shoulder, not by pressing. If you can feel a ridge on the back of the sheet, you are pressing too hard.
• Test on a scrap first: draw a line, erase it, then float a wash across where it was. If a dark line appears, lighten your hand.
• Avoid watercolour pencils for grid lines; they dissolve into the washes and stain the painting.

Use a kneaded eraser for the removal: it lifts graphite by pressing and pulling rather than abrading. A hard eraser scuffs the sizing, and a scuffed patch takes colour differently from the paper around it.

Paint and Brushes

Paint. Pigment choice matters more in the first layers than in the last. Phthalo Blue (PB15) is a staining pigment: it drives into the fibres and will not lift out again. Ultramarine Blue (PB29) is non-staining and granulating, so it settles into the paper's texture and lifts back with a damp brush. Cadmium Yellow (PY35) is opaque and covers what lies underneath rather than glowing through it. Put the lifting pigments down first, and keep the stainers for the last darks.

Brushes. Small rounds in sizes 2 to 6 work inside a single cell; a flat carries a wash across several.

Masking fluid. If part of the painting has to stay pure white paper, mask it before the first wash. Apply it with an old brush or a silicone shaper, never with good sable, because the latex sets hard in the ferrule and destroys the brush. Put it on dry paper only. Let it dry by itself rather than with a hairdryer: heat bonds it to the sheet permanently. Take it off within a day.

For watercolour sheets, use GridMyPic's Grid on Canvas mode: pick your real paper size (A4, A3 or custom dimensions in centimeters or inches) and export a PDF that prints at exactly that size. Measure one cell with a ruler to verify. Set up your sheet in the grid maker.

Grid the Reference

Reference and paper get the same number of equal cells, which gives both a shared coordinate system. Overlaying the grid digitally is quicker: our image grid maker does it from an uploaded photo. The physical alternative is clear acetate laid over the print, ruled with a permanent marker.

The number of cells has to match. The size does not: sixteen divisions across a six-inch reference and sixteen across a ten-inch sheet enlarge the image and leave every proportion intact.

How fine depends on the subject. Botanical work wants half an inch or smaller, because leaf venation and petal edges need more reference points than a broad shape does. Landscapes take one to two inches. Portraits want three-quarters of an inch to an inch, which works out at roughly eight to ten divisions across the width of the head, measured cheekbone to cheekbone. For a still life, size the grid for the hardest object in the group.

Whatever the number, keep every cell the same size. A grid with fine cells over the flowers and coarse ones over the background has stopped being a measuring instrument.

Transfer, Then Erase

Rule the paper grid first. Mark the divisions along all four edges, then rule between opposite marks rather than measuring each line individually, and label the coordinates in the margin so you can name a cell instead of counting to it. Then measure both diagonals: if they are not equal the grid is skewed, and every measurement you take from it carries that error.

Transfer one cell at a time, major shapes across the whole drawing before any detail. Keep the pencil at the pressure you tested on the scrap, and step back every few cells, because proportional errors are invisible at reading distance and obvious from two metres.

Then stop and erase, before any paint touches the sheet. Not "lighten to faint guides": erase. The last section explains what happens if you skip this.

Never spray fixative to hold the drawing down. Fixative resists water. A wash laid over it beads up and dries blotchy and uneven, and there is no version of this that works under watercolour. Mask the whites instead, and plan the painting order light to dark before the first wash.

Paint Across the Grid, Not Inside It

The grid did its work in the drawing. It should have no authority over the painting.

Wash across the cells. Plan each wash by the shape it covers, not by the cells it crosses, and keep a wet edge. Watercolour dries at the boundary where you stopped, so stopping at a cell line puts a hard edge exactly where the painting needed continuity. Mix more paint than the passage looks like it needs: a wash that runs dry halfway is the other common source of a seam, and a second mix will not match the first.

Work cell by cell only for isolated detail. A flower centre, an eye, a single leaf: something surrounded by dry paper on every side. Let each one dry before you start the one beside it.

Keep the gridded reference in view throughout, with a pointer on the cell you are reading from. What you are checking now is value and colour; placement was settled in the drawing. Build in three passes: light washes, then middle values, then darks and accents. Assign each area a value from one to ten before mixing anything. A painting with the right values in the wrong colours still reads as its subject. The reverse does not.

When It Goes Wrong

Problem: grid lines showing through the finished washes

Once a wash has dried over graphite, the gum arabic that binds the paint has sealed the pencil into the surface. It is not a stubborn line, it is a line that is no longer on top of the paper, and yellows seal hardest. Scrubbing at it with a damp brush lifts the paint and leaves the graphite, so you end up with a pale stripe and the line.

The only reliable fix is upstream. Erase the grid completely, before any paint touches the sheet:

1. Transfer the drawing square by square, then stop.
2. Lift the grid lines off with a kneaded eraser, dabbing rather than rubbing, until nothing of the grid remains. Keep only the contours of the subject.
3. Hold the sheet at a low angle to a window. Anything you can still see will be visible in the finished painting.

Two habits make step 2 easy. Use the pencil lines as a guide, not an edge: paint up to a line rather than over it, and whatever survives stays liftable. And erase as you go, clearing the pencil you no longer need before the next wash covers it.

If a line has already been sealed in, you have three honest options and none of them is invisible: glaze a darker passage over that area so the line disappears into it, cover it with a touch of white gouache and repaint, or leave it. A visible construction line is not a ruined painting, but pretending it can be scrubbed out is how a good painting gets a hole rubbed in it.

Problem: stiff, mechanical results

Values jump at the cell boundaries, or the brushwork has one character everywhere. Both come from treating the grid as a painting boundary rather than a drawing aid. Vary the brushwork across the lines, save the loosest passages for after the grid is gone, and let atmospheric backgrounds ignore the structure entirely.

Problem: proportions that came out wrong anyway

Check the grid before you blame the transfer. Unequal diagonals, a miscounted division, and a reference grid with a different number of cells from the paper grid all produce the same symptom. Once painting has started you cannot re-measure: extend an element past where the grid said it ended, let the composition absorb the discrepancy, and check both diagonals before you rule the next grid.

Charcoal: Draw the Grid in the Medium, Then Fix It

Charcoal is a blunt instrument. A stick held on its side lays down a mark two or three centimetres wide, which is why it can cover a sheet in a minute and why a nose can drift half an inch before you notice. A grid takes the placement off your hands, so all of your attention goes into value, which is what charcoal is for.

The trade-off runs the opposite way from pencil. Graphite gives you a precise line immediately and you spend the next hour finding the value. Charcoal gives you the value almost at once, and the precision is what you have to build in beforehand. That is the grid's job here: it tells you which square the eye corner sits in, so you never have to ask a stick of willow to be accurate.

This part assumes you can already draw a grid and scale it to your paper. If not, the complete grid drawing guide covers the mechanics, and you can generate one from your own photo with our grid for drawing.

The four charcoals, and which one each job wants

They are not interchangeable, and the difference that decides most of it is whether there is a binder in the stick.

Willow and vine. Willow is the lightest charcoal there is, which is exactly what you want for construction lines. Vine goes a shade blacker. Both are binder-free, which is why the grid gets drawn with them: a line with no binder lifts off with a kneaded eraser and leaves the paper untouched. Buy medium-thickness willow.

Compressed charcoal. Charcoal powder pressed into sticks with a gum or wax binder. It gives you blacks that willow cannot reach, and it commits: the binder drives the particles into the tooth of the paper and a kneaded eraser will not pull them back out. Keep it for the darkest passages and apply it late.

Charcoal pencils. Charcoal in a wooden or paper casing, graded Hard, Medium and Soft, though some brands print HB through 6B instead. This is the only charcoal that will draw an eyelash, and the right tool for reinforcing grid intersections once the sticks have buried them.

Powdered charcoal. Loose powder applied with a brush, a chamois (a soft suede-like leather cloth) or your fingers. Powdered charcoal on a wide soft brush covers several cells in one stroke, which is how you get an even background without visible stick marks.

White charcoal, despite the name, is chalk (calcium carbonate) with a binder. It sits on top of black charcoal rather than mixing into it, so use it for the last two or three highlights on toned paper, not for lightening an area you overdid.

What paper, and how coarse should the grid be?

Charcoal needs tooth: enough surface texture to hold the particles. Weight matters less than most people assume. Paper is sold by gsm, grams per square metre, and for dry media that number tells you how well a sheet survives repeated erasing rather than how the charcoal sits on it. Strathmore 500 Charcoal is 95 gsm and takes charcoal well; Canson Mi-Teintes is 160 gsm, with a pronounced honeycomb tooth on one side and a smoother surface on the other. Copier paper is the one to avoid: there is nothing for the particles to lodge in, so the second layer slides over the first.

A mid-grey or cream sheet hands you a middle value to start from: you work down into it with charcoal and up out of it with an eraser or white chalk, and grid lines stay visible on it far longer than on white.

The carbon itself does not fade: it is the same substance as the pigment in ivory black paint. What ages is everything around it, meaning the gum or wax binder in compressed charcoal, and the paper. Buy paper that says acid-free or neutral pH on the pad and the drawing outlives you.

How coarse should the grid be? Coarser than you would use for pencil. A stick of charcoal held on its side lays down a mark two or three centimetres wide, so a cell smaller than that stops being a target and starts being a box you colour in. For a head-and-shoulders portrait on an 8x10 inch sheet, 8x10 cells of about one inch each puts an eye inside roughly one cell: a misplaced pupil becomes a one-cell problem instead of a whole-face problem. Go finer only where you are working in charcoal pencil. For a figure, 6x8. For a landscape, 4x6.

The same portrait in graphite takes a denser grid, and portrait drawing with the grid method uses 10x12 for it. That is a difference of medium rather than a disagreement about method: a 2H pencil can hit a target charcoal cannot even see.

Draw the grid itself with willow, at the lightest pressure that still leaves a line you can follow. A hard graphite line stays visible under charcoal for longer, but pressing graphite into paper burnishes the tooth flat, and charcoal will not sit on a burnished line. Willow you have to reinforce twice is the smaller problem.

Map the values into the squares before any charcoal touches the paper

Run the reference through GridMyPic's Outline Studio first. The extracted contour map shows where the hard and soft edges sit, so you know in advance which squares carry a crisp boundary and which dissolve into tone. Extract the outline here.

Then give every square a number. Use the Munsell direction, where 10 is white and 1 is black, because that is how bought value scales and value finders are printed, and an inverted map is worse than no map. Some teachers number the other way, so the first thing to check on any scale you buy is which end the 1 is on.

Write the numbers on the reference print, not on the drawing. Most squares hold more than one value: record the dominant one and note the exception beside it.

One thing to hold on to while you assign numbers: a rough surface reads darker than a smooth one under the same light, because the light bounces around inside the texture and gets absorbed instead of coming back to you. This is why bark and silk lit identically are not the same value. Assign numbers from what the reference actually shows rather than from what you know the material to be, and this is the effect you stop missing.

Mark the highlights with tiny dots before any charcoal goes down. Paper white you never covered is brighter than paper white you erased back to.

Four passes, in this order

1. Block in the masses. Hold the vine stick on its side at a shallow angle. The whole length contacts the paper and you get flat, even coverage across cells instead of a stroke. Aim for the middle of the range everywhere, with nothing near black yet, and ignore every internal detail. What you want out of this pass is a drawing where the big shapes are already in the right squares.

2. Separate the middle values. This is where the form appears, and it decides whether the drawing works. Compare each square against its neighbours, not against the reference in isolation: a value is only right relative to what surrounds it. Powdered charcoal on a brush or a chamois handles the broad transitions, a vine stick anything with an edge.

3. Put in the darks. Compressed charcoal, applied to the few places that genuinely need it: the pupil, the nostril, the shadow under the jaw, the gap between two folds. Charcoal's intensity means the darks arrive faster than you expect and cannot be undone, so put in half of what you think you want and look again from three metres away.

4. Take out the lights. A kneaded eraser moulded to a point lifts soft highlights; a vinyl eraser cuts a hard one. Work from your dotted marks rather than hunting for highlights afterwards. While you have the kneaded eraser in hand, dab out any grid lines still showing in open areas, because shading over them traps the line where it can never be removed.

Expect the value work to take longer than everything else combined, and expect the last ten minutes to be about stopping rather than adding.

Fixative darkens your lights, so spray it knowing that

One thing to know before the first spray: fixative darkens what is already on the paper, and it takes the lightest values down hardest. Your erased highlights are the first casualty. Spray in several very light passes rather than one wet one, from 12 to 16 inches (Krylon's own figure on the Workable Fixatif can), and do the highlights after the last coat, not before it. Test on a scrap of the same paper first, because the shift varies between brands.

Workable fixative is formulated so you can keep drawing over it. Final fixative seals the surface and nothing more goes on top of it. For anything unfinished, use workable. Two or three passes, each barely wetting the surface, then give it fifteen minutes before you go back in.

Dust management. Hold the sheet vertically and tap the back of it so the loose charcoal falls off; do not blow it off and do not use a can of compressed air, because that is the main way charcoal dust ends up in your lungs rather than on the floor. Wipe margins with a soft brush or a damp cloth rather than a dry one, which just moves the dust around. The same reason applies to fixative: spray it outdoors or at an open window, not over the desk.

Keep your hand off the surface. A mahl stick, a rod with a padded ball at one end that rests against the edge of the board, holds the drawing hand clear; a clean sheet under the heel of your hand does the same job for less. Store the finished drawing flat with a sheet of glassine over the face, or the charcoal prints itself onto whatever sits above it.

Charcoal on canvas: the underdrawing for an oil painting

Charcoal is the traditional way to get a gridded drawing onto primed canvas. Draw the grid with thin willow rather than pencil, at a pressure that leaves it barely visible, and plot the drawing with the same lines you would use on paper. The advantage over pencil is that a rag takes the whole thing off and you can start again.

Do you need to seal it? Usually not, and the sealing is the riskier half. Charcoal is chemically close to ivory black oil paint, so it does not fight the paint. What it does do is lift as loose dust and grey your first light passages. Knock the excess back before you paint, with a light swipe of a paper towel until only a faint line survives, and paint straight onto that. If you still want it fixed, one very light pass of workable fixative is enough.

Four ways a charcoal grid drawing goes wrong

It has gone muddy. The symptoms are a slick surface, a kneaded eraser that lifts almost nothing, and squares that used to differ now reading as one grey. The cause is too many passes over the same tooth. Lift a whole region back, spray one light coat of workable fixative for a fresh surface, and rebuild with fewer, firmer decisions.

You can still see the squares. Values jump at the cell boundaries because each square was finished as a self-contained unit. Use the grid for placement and the block-in only. From the middle-value pass onward, work strokes that deliberately run across the lines.

The grid has disappeared. Reinforce intersections rather than whole lines, with a charcoal pencil or a hard graphite pencil, and only where you still need a measurement. Photographing the drawing at the block-in stage gives you a record of where the lines were, which is usually enough to recover a landmark without touching the surface at all.

The face reads as parts stuck onto a head. Two habits cause most of it. Do not outline the lips, because a line round a lip reads as a lip-shaped object stuck on the face; model it with value change and the mouth sits in the skin. And work vine charcoal into the tooth for the hair mass first, then put in ten or fifteen strands with a pencil. Drawing every strand reads as wig.

Your next drawing: ten squares, white to black

Rule a row of ten squares, each about an inch, and number them 10 down to 1 so the row reads the way a bought value scale does. Leave square 10 as bare paper. Fill square 1 with the blackest compressed charcoal you own, pushed as far as it will go. Then work the eight steps between them so the jump from any square to the next is the same size.

It is harder than it sounds. Most people hold five or six distinct steps before the middle collapses, and square 1 is almost always dark grey rather than black. Use the paper you plan to draw on, since the same stick reads differently on different tooth, and keep the strip beside you while you number the reference. It turns "this square is dark" into "this square is a 3", which is the only version of the instruction you can act on.

For complementary studies, explore botanical drawing with grids and portrait drawing with the grid method.