Bargue drapery plates
The folds of cast drapery are pure curve; diagonal cells gave students the crossings the plain grid lacked.
Artist guide · the croisillons upgrade · nine points per cell
Diagonal cell grid
A plain transfer grid leaves you guessing inside each cell — a curve has to be eyeballed across an empty square. The diagonal-cell grid fixes that by drawing diagonals through every cell, turning four corner points into nine: the corners, the four edge midpoints where the diagonals cross, and the cell centre. Curves and angles now snap to predictable crossings instead of floating. It is the 19th-century French atelier upgrade known as croisillons, "little crosses," used to copy the curve-heavy Bargue plates — and almost never printed in modern how-to books. Here is the math of nine points, the verified history, and how to use it on the subjects that need it.
- Construction
- Transfer grid + diagonals per cell
- Reference points
- 9 per cell (vs 4)
- Atelier name
- Croisillons
- Difficulty
- Beginner
- Best for
- Curves & oblique angles
- Also known as
- Diagonal grid method
See the diagonal-cell grid on five subject categories
‹›
On a portrait, the diagonals in the central row give the curve of the cheek and the line of the brow a set of crossings to snap to — the cell centre and edge midpoints replace the guesswork of an empty cell.
What the overlay shows
The diagonal-cell overlay draws the same labelled square grid as the proportional transfer grid, then adds diagonals through each cell. With both diagonals the lines cross at the cell centre and meet each edge at its midpoint, giving nine reference points per cell instead of the four corners alone. A single-diagonal mode is available for less visual busyness, and individual cells can stay plain.
For a curve passing through a cell, the diagonals tell you exactly where it crosses the diagonal lines, where it meets the edge midpoints and whether it runs above or below the cell centre. For an oblique line, the diagonals provide a ready 45-degree reference to read the angle against. This is what makes the diagonal grid method a grid method for curves: the cell stops being "approximately copy what's inside" and becomes "snap this curve to these specific reference points" — the change that makes the difference on hair, drapery and organic form.
The math: why nine points
A plain cell offers four reference points — its corners. Adding both diagonals adds five more, and the gain compounds for curved content:
4 corners + 4 edge midpoints + 1 centre = 9 reference points per cell
- Curves need three points to define an arc. Four corner points barely fix one arc per cell; nine points fix several and let you read the curve's direction at each crossing, not just its endpoints.
- The midpoints are the new information. The four edge midpoints, created where the diagonals meet the cell edges, are exactly the places a curve tends to cross — so they catch the part of the shape the corners miss.
- A single diagonal is often enough. One diagonal is the simplest way to subdivide a square cell: it splits the cell into two triangles and adds reference without the full X's clutter; alternating its direction between cells makes a chevron texture that surfaces placement errors.
The practical result is roughly a one-third to one-half accuracy improvement on curve-heavy passages at the same cell count. Try it in the live tool — toggle between single and double diagonals and watch the snap points change.
History — what is real and what is myth
Verified history (with primary sources)
Renaissance roots. Diagonal subdivision of a transfer grid descends from the same workshop measurement tradition Dürer documented in Underweysung der Messung (1525); adding a diagonal to refine a cell is a small, natural extension of the gridded screen, part of the broader workshop transfer practice Carmen Bambach documents.17
19th century — the ateliers. The diagonal-cell upgrade appears in French and Italian atelier teaching as croisillons, used to copy the curve-heavy Bargue plates. Charles Bargue's Cours de Dessin (1866–71) used diagonal subdivision on some advanced plates to support cell-interior detail, as Gerald Ackerman's study of the plates records.26
20th century — the plain grid won the books. Mainstream how-to authors — Bridgman, Hale and others in the Art Students League lineage — taught the plain grid and sight-measurement, and the diagonal variant stayed an atelier specialism rather than a published standard, even as Ruskin's drawing pedagogy reached a wide readership.348
Today — the contemporary ateliers. Programmes such as the Florence Academy, Grand Central Atelier and Watts Atelier keep the croisillons tradition alive; students meet it when they reach the elaborate figure studies that need finer cell-interior reference. Betty Edwards's account of why isolating shapes defeats symbol substitution explains the underlying perceptual gain.5
Unverified claims that won't die
"Nine points make the drawing nine times as accurate." Overstated. The accuracy gain is real but modest — roughly a third to a half on curve-heavy cells — and it depends entirely on the subject. On flat, simple content the diagonals add nothing.
"Croisillons is a secret professional technique." It is obscure, not secret. It simply never made the popular how-to books; it is openly taught in ateliers and easy to add to any grid.
"More diagonals are always better." No. Past a single diagonal, or two on the busiest cells, the lines start competing with the subject's own contours and the grid becomes harder to read than the drawing it is meant to help.
When to use it (and when not)
| If you want to... | Use diagonal-cell | Don't use it for... | Difficulty |
|---|---|---|---|
| Snap a curve accurately | The diagonals give crossings the curve lands on instead of empty cell interior | Flat horizontal-and-vertical content (the plain grid is cleaner) | Beginner |
| Copy hair, drapery or foliage | Nine points per cell handle organic detail the corners miss | Simple graphic shapes with no curves | Beginner |
| Read an oblique angle | The 45-degree diagonals are a ready reference to measure against | Subjects you can already draw accurately freehand | Intermediate |
| Keep the grid readable | Use a single diagonal, alternating direction, for reference without clutter | Reproduction needing both diagonals everywhere (use cross-diagonal) | Beginner |
| Apply detail only where needed | Leave simple cells plain and add diagonals to curve-heavy ones | Whole-canvas uniform precision (use a finer plain grid) | Intermediate |
Where diagonal-cell actually appears
Six places the croisillons upgrade does demonstrable work — wherever curves and angles defeat the plain grid.
Portrait hair masses
Hair flows in sweeping curves; the diagonal crossings keep the locks from drifting cell to cell.
Organic landscape forms
Soft repeating curves are where freehand proportion drifts most; the diagonals pin the turns.
Leaning figures & oblique architecture
The 45-degree diagonals give an angle to read a tilted spine or a foreshortened roofline against.
Tattoo & lettering curves
Flowing script and ornamental scrolls transfer cleanly when each curve has crossings to land on.
The nine-point demonstration
One cell, both diagonals: four corners, four edge midpoints, one centre — the nine snap points made visible.
Common mistakes
1
Adding diagonals to every cell by reflex
Filling flat, simple cells with diagonals buries the subject under lines that carry no useful information, making the grid harder to read than the drawing.
Fix: add diagonals only to the curve- and angle-heavy cells; leave plain content plain.
2
Ignoring the edge midpoints
Using the diagonals only as decoration and still reading from the corners throws away the very points — the edge midpoints — that a curve most often crosses.
Fix: read each curve against where it meets the diagonals and the edge midpoints, not just the cell corners.
3
Reaching for the full X when one diagonal would do
Both diagonals on every cell is reproduction-grade density that most organic subjects don't need, and it slows reading without improving the result.
Fix: default to a single alternating diagonal; escalate to the cross-diagonal grid only for true precision work.
How different disciplines use it
For painters
The diagonal-cell grid is the portrait painter's answer to hair and drapery. Run a plain transfer grid for the overall block-in, then add diagonals to the cells carrying curves so the locks and folds snap to crossings rather than drifting. A single alternating diagonal usually does it; keep the full X for the few cells where the contour is genuinely complex. It is the croisillons upgrade the ateliers used on the hardest Bargue plates.
For students
If your gridded copies are accurate on straight features but wander on curves, this is the fix. The diagonals give the curve somewhere to land — the edge midpoints and the cell centre — instead of an empty square to guess across. Learn it as the next step after the plain grid, exactly where contemporary ateliers introduce it: when the figure study gets curve-heavy.
For tattoo artists
Flowing script, ornamental scrolls and organic blackwork are all curve, and transferring them to a stencil or to skin is where proportion slips. The diagonal crossings give each sweep a set of points to pass through, so the design lands the same size and shape it was drawn. Add diagonals to the busy cells of the flash and leave the open areas plain.
For landscape painters
Foliage, hills and water are soft repeating curves — the content freehand proportion drifts on most. A diagonal in each curve-heavy cell pins where a ridge line turns or a tree mass bulges, and an alternating direction makes errors easier to spot. For an oblique architectural element in the scene, the 45-degree diagonal gives an angle to measure the tilt against.
"The hardest thing for the beginner is the curve, because the eye supplies a curve it expects rather than the one that is there; a reference point on the line is the cure."
Robert Beverly Hale, Drawing Lessons from the Great Masters (1964)4
Frequently asked questions
Why add diagonals to a transfer grid?
A standard square grid gives four reference points per cell — the corners. Adding diagonals adds four edge midpoints where they cross the cell edges plus the cell centre, for nine points per cell. The extra points let curves and angles snap to predictable locations instead of being eyeballed across an empty cell interior, which sharply improves accuracy on organic subjects.
When should I use diagonal-cell instead of a plain grid?
Use diagonal-cell when the reference has a lot of curves — hair, drapery, organic landscape forms — or oblique angles such as leaning figures and architecture seen at an angle. The diagonals give snap points exactly where curves and angles need them. For simple subjects with mostly horizontal-and-vertical content the plain grid is faster and less visually busy.
Where does the diagonal-cell variant come from?
It appears in 19th-century French and Italian atelier teaching under the name croisillons ("little crosses"), used alongside the Bargue plates as an upgrade for students struggling with curve-heavy studies. It never entered mainstream 20th-century how-to books, which kept the plain grid, so it remains relatively obscure outside atelier-trained painters.
How is diagonal-cell different from cross-diagonal?
Diagonal-cell is the curve-snapping atelier variant, typically run with a single diagonal or a light X to add reference inside curve-heavy cells. The cross-diagonal grid always draws both diagonals through every cell for maximum sub-cell precision and reproduction work. Diagonal-cell favours readability and organic subjects; cross-diagonal favours precision at the cost of visual density.
Does the overlay show single or double diagonals?
Both are available. The default X (both diagonals) gives the canonical nine-point reference per cell; a single-diagonal mode is less busy with seven points per cell, and a no-diagonal mode leaves chosen cells plain so you can apply the diagonals only where curves and angles actually need them.
Why does one diagonal per cell often hit the sweet spot?
A single diagonal splits each cell into two triangles and adds enough reference to handle most organic detail without the visual noise of the full X. Many artists set the diagonals to alternate direction between adjacent cells, producing a chevron texture that catches placement errors better than a uniform direction.
Can diagonal-cell be combined with other overlays?
Yes. It is built on the plain proportional-transfer grid, so it stacks with the same labelled cells, steps up to the cross-diagonal grid when you need both diagonals everywhere, and scales onto walls through the mural-scaling variant. For figures you can pair it with fixed measurement to count head-heights alongside the cell reference.
How do diagonals help with grid drawing?
A plain grid only fixes the corners of each cell, so anything that happens inside the square has to be eyeballed. The diagonals add the edge midpoints and the cell centre as reference points, which is where curves and oblique lines tend to cross. Reading each curve and slope against those crossings rather than across empty space makes for a more accurate grid transfer method — particularly for angles and slopes, where the 45-degree diagonal gives you a fixed line to measure the tilt against.
How do you draw curves with a grid?
Apply the diagonal grid method over your reference, then for each curve note where it crosses the diagonals, the edge midpoints and the cell centre. Plot the same reference points on your surface and draw the curve through the crossings rather than copying the shape freehand inside the cell. Because a curve needs at least three points to define its arc, the extra points per cell let you snap curves into place instead of approximating them.
References
- Dürer, A. Underweysung der Messung (Course in the Art of Measurement) (1525). Trans. as The Painter's Manual, W.L. Strauss. Abaris (1977). ISBN 0-913870-23-5.
- Bargue, C. & Gérôme, J-L. Drawing Course (Cours de Dessin) (1866–71). Ed. G. Ackerman, ACR Édition (2003). ISBN 2-86770-128-6.
- Bridgman, G.B. Constructive Anatomy (1920). Reprint: Dover (1973). ISBN 0-486-21104-5.
- Hale, R.B. Drawing Lessons from the Great Masters. Watson-Guptill (1964). ISBN 0-8230-1401-4.
- Edwards, B. Drawing on the Right Side of the Brain. J.P. Tarcher (1979; rev. 2012). ISBN 0-87477-419-5.
- Ackerman, G. Charles Bargue and the Art of Drawing. ACR Édition (2003). ISBN 2-86770-152-9.
- Bambach, C. Drawing and Painting in the Italian Renaissance Workshop: Theory and Practice, 1300–1600. Cambridge University Press (1999). ISBN 0-521-40218-2.
- Ruskin, J. The Elements of Drawing (1857). Reprint: Dover (1971). ISBN 0-486-22730-X.
Other Artist Guide overlays
Notes from the studio · Three practitioners on the diagonal-cell grid
Illustrative composites of how the tool gets used in practice — not quotes from named individuals.
Plain grid for the block-in, diagonals only on the hair. The croisillons cell is the difference between locks that read and locks that wander.
I introduce croisillons exactly when the Bargue plates get curvy. Students stop guessing the fold and start reading where it crosses.
Free and browser-only means I can toggle single and double diagonals on any machine until the curve snaps where I want it.
Open the diagonal cell overlay
Drop a reference image. The diagonals apply through each cell in one click. Free, in your browser.
Launch Grid Maker Pro →