Getting the Drawing on the Wall
How do you get a sketch onto a wall?
A muralist usually starts with a drawing and has to scale that to the larger surface the muralist is going to paint. There are multiple techniques for doing so, and while some older techniques are still being used today, new technologies have pushed methods into new directions.
Pouncing
The oldest reliable method is pouncing. The artist makes a full-scale preparatory drawing on a single or multiple sheets of paper or cloth. This is called a cartoon. Usually, a smaller sketch is redrawn and enlarged into the full-scale drawing. Then, with a needle or a spiked wheel called a pounce wheel, small holes are pricked along every contour line in the drawing. The cartoon is held against the wall and a porous bag of charcoal dust or powdered pigment is tapped along the perforated lines. The dust passes through the holes and leaves a dotted outline on the surface, creating a sketch on the wall which the artist can follow.
In the Italian fresco tradition the technique was originally called spolvero, from the word for dust. Raphael used it, and so did Michelangelo, selectively, for the Sistine Chapel ceiling. The technique moved across Europe and throughout centuries essentially unchanged. American muralists and sign painters in the 1930s and 1940s used it routinely, calling it pouncing rather than spolvero, and the English name stuck. It works on any surface, preserves the cartoon for reuse, and it gives you a one-to-one copy of the design on the wall. Artists today still use it for exactly those reasons.
The technique is relatively time consuming. For murals that cover the insides or outsides of a building, or the entire ceiling of the Sistine Chapel, there are quite a lot of holes to make. Most professional muralists and sign painters today use an Electro Pounce Machine, which is a stylus tool that perforates paper with an electric charge. An Electro Pounce Machine requires a power box to regulate an electric spark, a stylus to guide the spark, and a grounding plate (sheet of metal) to complete the electrical circuit. A sheet of paper is placed on the grounding plate, and holes are made on the paper by the charge between the grounding plate and the stylus. Fundamentally, this process of perforating sheets of paper is the same that was used by the old masters.
Incising into Plaster
Fresco painters also developed a faster alternative that skipped perforation. While the final coat of plaster, the intonaco, is still wet, a cartoon is pressed against the surface and the artist traces the major contour lines by pushing down on the paper with a pointed stylus. The pressure leaves shallow grooves directly in the plaster. The cartoon is removed and the incised lines remain as a permanent guide, embedded in the surface itself. On surviving frescos which used this technique, you can still see the grooves that were left.
This technique worked only in fresco, because it required wet plaster soft enough to take the impression. And it was limited to the area plastered that day, the giornata. Each new section of intonaco got its own tracing session. On the Sistine ceiling, you can see two techniques in use. Michelangelo pounced some sections and incised others, depending on the complexity and his confidence with the forms. The architectural elements, which had long straight lines, were incised. The figures, which required subtler curves, were more often pounced.
Incising was faster than pouncing but less forgiving. A wrong line pressed into wet plaster couldn’t be erased. And if the plaster started to set before the tracing was finished, the stylus would tear the cartoon rather than impress. The method required a plasterer and a painter working in close coordination, the plasterer gauging how much wall to prepare, the painter gauging how fast the tracing could be done.
The Grid
A simpler approach, and one that didn’t require a full-scale cartoon at all, was the proportional grid. The artist drew a grid over the small sketch and a corresponding grid, at the target scale, on the wall. Then each cell was copied individually, translating the small drawing to the large surface one rectangle at a time.
This is old. Leon Battista Alberti described it in the fifteenth century. It was the standard method for scaling up in mural workshops for centuries and remained common well into the twentieth. Thomas Hart Benton used gridded studies for his mural work. The method’s advantage is that it requires no specialized equipment and scales to any size. Its disadvantage is that it’s mechanical. The drawing gets translated through a series of local decisions, cell by cell, and the continuity and proportions of the original sketch risk imperfection.
Some muralists combine the grid with pouncing, using the grid for composition and layout, then pouncing for the important details. Another variation that some muralists use today is drawing random lines on the wall first, taking a picture of the wall, and overlaying the picture of the scribbled wall onto a digital design. The scribbles become a guide which the artist can follow to know the placement of contours.
Projection
Overhead projectors changed the equation entirely. Instead of building a full-scale cartoon and physically transferring its lines, the artist can project a transparency of the design directly onto the wall and trace the projected image with pencil or chalk.
This technology existed in rudimentary form, as the camera obscura, for centuries. But the practical shift happened in the second half of the twentieth century, when electric projectors became cheap, bright, and portable. By the 1970s and 1980s, muralists working on exterior walls in cities, particularly in the community mural movements in Chicago, Los Angeles, and Philadelphia, were using overhead projectors and later slide projectors as standard tools. Kent Twitchell’s monumental photorealist portraits on Los Angeles buildings in the 1970s and 1980s relied on projection from photographic slides.
Digital projectors extended this further. A muralist today can take a digital file, connect a projector to a laptop, and throw the image onto a wall at whatever scale the throw distance allows. The projection can be adjusted, resized, repositioned. If the wall has irregular geometry, the software can keystone-correct the image to compensate, or edits can be made to the digital file.
The process of projection is much faster than pouncing, because the sketch only has to be done once, directly on the wall. The tradeoff is a dependence on conditions. Projection requires darkness or at least low ambient light, which limits outdoor work to nighttime sessions. It also requires access to electricity and a stable setup.
Augmented Reality
The newest development is augmented reality. With a passthrough headset like the Meta Quest, a muralist can overlay a digital drawing directly onto the real wall. The drawing appears anchored to the surface at the correct scale, visible through the headset while the artist traces it with pencil or chalk.
AR works like projection without the constraints. There is no projector to set up, no darkness required, no throw distance to calculate. The overlay stays locked to the wall regardless of ambient light. The artist can walk up to the surface, trace a section, step back to check it, and return without losing registration. If the wall has curves or corners, the overlay can be mapped to the geometry.
This is currently the newest technology for the application of a design to a wall. The headset has a battery life, and to be honest, isn’t the most comfortable thing to wear for a period of time, so it is best used for just applying the sketch. The transfer itself is faster than any of the previous methods, since the sketch is on the wall as soon as the headset is on.