Hatching (hachure in French), In drawing and engraving, as in painting, hatching is the line of a set of straight or curved lines that is used to produce a shade of half-tone, not an outline.

Hatching is an artistic technique used to create tonal or shading effects by drawing (or painting or scribing) closely spaced parallel lines. (It is also used in monochromatic heraldic representations to indicate what the tincture of a “full-colour” emblazon would be.) When lines are placed at an angle to one another, it is called cross-hatching.

The hatch pattern has existed since prehistory, both in drawing and in pottery decor, either as a decorative motif or as a drawing technique.

In engraving and drawing, the role of hatching is to produce different gray values, depending on their thickness and density relative to the white of the support. The hatches are not perceived as individual entities of the drawing, but as a set giving the perception of a shade or shade more or less uniform or degraded. The hatching, drawn to follow the curvature of the object represented, brings closer, a close view, a volume information in addition to that of value. In some widely spaced hatch patterns, as in Leonardo da Vinci, this form information is the main effect.

Hatching is especially important in essentially linear media, such as drawing, and many forms of printmaking, such as engraving, etching and woodcut. In Western art, hatching originated in the Middle Ages, and developed further into cross-hatching, especially in the old master prints of the fifteenth century. Master ES and Martin Schongauer in engraving and Erhard Reuwich and Michael Wolgemut in woodcut were pioneers of both techniques, and Albrecht Dürer in particular perfected the technique of crosshatching in both media.

Artists use the technique, varying the length, angle, closeness and other qualities of the lines, most commonly in drawing, linear painting and engraving.

The hatching is used especially when the technique does not make it possible to obtain halftone and shades otherwise, as is the case with the drawing with the pen or the engraving on wood, the chisel, the etching or the intaglio, among others. In this case, we have only solid lines of the color of the ink (black, most often). To obtain grays, we proceed by hatching: fine and spaced, they give a light gray, thick and tight, a dark gray. The hatches are parallel, they can be superimposed and crisscrossed to give more density. Their appearance varies according to the technique: relatively broad wood engraving of wire, they become extremely fine with the end-to-nineteenth-century woodcut, during which the use of the striped stall or bicycle spreads, a kind of multi-toothed chisel for engraving as many parallel hatches in one jet. They are fine and substantially equal with copper engraving tools that only “scratch” the surface (etching, intaglio, some uses of the chisel), and are then crossed.

They can also be of variable thickness (wood engraving, chisel) when the tool can dig more or less deeply the support, and give a smooth gradient effect.

Hatching is not necessary with techniques that make it possible to obtain halftones directly, such as painting, aquatint or grained stone lithography.

The hatch pattern is used, however, either for its simplicity and speed of execution, or to indicate the volume by a suitable curvature of the hatching lines. In pencil, although the grain of the paper makes it possible to modulate the value without visible features, it is often preferable to hatch to obtain grays. The process maintains the vigor, spontaneity and freshness of the drawing, unlike flat drawing or fading, which is more laborious.

In painting, the hatching is used as in drawing, or as a basis for a smooth rendering obtained, later, by glazes. We distinguish the hatchings of the English drawing, of uniform direction and which do not cross, varying the value by the spacing and the size of the lines, and the hatching with the Italian, which, according to the expression of Watelet must vary so that they always indicate the inflection or the general form of the different objects which they serve to paint. The hatching, in painting, is of course in color.

In technical drawing, hatching is a line of constant thickness, parallel and equidistant, which has a conventional role of indication. They were drawn manually using a hatching device or on a drawing table with a drawing device.

In a definition pattern, regardless of the material, the hatching is in continuous line at an angle of 45 ° or 30 ° to the edges of the sheet.

In an overall drawing, hatching is distinguished by a pattern associated with a type of material and more generally with a physical or technical property. On each view, the same part must have the same pattern (orientation and frequency). If possible, vary the orientation of the hatching between two joint pieces.

Between the 1970s and the generalization of computer science, textures were often made using frames: adhesive films bearing in print, which were cut and glued in the desired places. For complicated contours, simple hatching with hatching was faster.

The main concept is that the quantity, thickness and spacing of the lines will affect the brightness of the overall image, and emphasize forms creating the illusion of volume. Hatching lines should always follow (i.e. wrap around) the form. By increasing quantity, thickness and closeness, a darker area will result.

An area of shading next to another area which has lines going in another direction is often used to create contrast.

Line work can be used to represent colours, typically by using the same type of hatch to represent particular tones. For example, red might be made up of lightly spaced lines, whereas green could be made of two layers of perpendicular dense lines, resulting in a realistic image.

In cartography, the hatching was used to indicate the reliefs on the staff maps or others, which were printed intaglio. Their use, codified over the years, made it easy to read a map: the hatches were parallel, arranged in the direction of the steepest slope, and of a thickness proportional to the inclination of the slope, according to a “tuning fork” determined mathematically.

Heraldry uses to describe a coat of arms a range of colors representing metals, enamels, furs, etc. In printed books, as it was rarely possible to have color representations, a conventional system of black-and-white hatching was adopted, with surfaces consisting of equidistant parallel lines giving a mean value of gray and identifiable by their orientation. the enamels: horizontal: azure (blue); verticals: mouths (red); horizontal and vertical crossed: sand (black); at 45 ° to the left (“in band”): sinople (green); at 45 ° to the right (“in bar”): purple (purple).

Linear hatching:
Hatching in parallel lines. Normally the lines follow the direction of the described plane.

Layers of hatching applied at different angles to create different textures and darker tones. At its simplest, a layer of linear hatching is laid over another layer at a 90° angle, to which further diagonal layers may be added. Other methods include layering arbitrary intersecting patches. Crosshatching in which layers intersect at slight angles can create a rippled moiré effect.

Contoured hatching
Hatching using curved lines to describe light and form of contours.