Drawing is the thread that ties together my occupations: I am a technician in the WACC department of paper conservation, as well as an artist and art instructor. My art practice focuses primarily on drawing, I teach drawing courses as an adjunct lecturer, and I have had the opportunity to observe a diverse range of drawings and works on paper in my time at the WACC. A recent discussion in the paper lab emphasized the intersection of drawing across these fields. Looking at a figure drawing with associate conservator, Brook Prestowitz, I began to scrutinize the image for ‘tick marks’ or underlying indicators of the artist’s approach to constructing the figurewhich sparked a conversation on the typical methods artists use to develop accuracy in drawing. Brook was interested in how a particular method of drawing might be evidenced in a completed image, and how this information could inform conservation efforts.
Conservators are necessarily invested in the tangible, material history of artbut how do conceptual or technical practices, throughout art history, inform artist decision-making and approach to art production?
These methods may or may not have immediate bearing on material choice or the physical properties of an artwork, but they help to breathe life into and shed light on the artist's thought process, training, and vision. Throughout much of art history, realism and mimesis have been paramount in artistic development, and at the foundation of this pursuit is the practice of objective life drawing.

Two Methods of Measurement

Objective drawing is aimed at realism and fidelity to nature—with the added benefit of a system by which to check or confirm that the placement, orientation or proportion of elements within a drawing are accurate. In short, it is a mathematical way to transcribe the visible world. Artists use basic geometry, often in the form of vertical, horizontal, and oblique angle lines, to establish relationships between points within a subject, as well as distance measurements and ratios, to reproduce their subject on paper with mathematical consistency. Objective drawing has been widely taught and utilized by academies and art schools as a way to teach students to see critically and think visually. One of the broadly applicable benefits of its practice is an understanding of the relationship between two-dimensional and three-dimensional space. Objective drawing’s persistence in academia is due in large part to this advantage; students pursuing both fine and applied arts—from photography to graphic design—equally benefit from a strong foundation in visual-spatial comprehension. Beyond simply sharpening the eye, objective drawing has been historically applied in the practice of figure drawing, as a way to capture the complexity of the human body. Its insistence on accuracy, and a system for checking accuracy, make it particularly well suited for the demands of rendering complex forms in space. 
There are two predominant schools of thought, or methods, of objective drawing: the sight-size method, and the comparative method. The historical origins of these methods are contested [1], but the sight-size method can be traced to at least the 17th century [2]. The comparative method may have antecedents in Renaissance art, where proportional ratios were emphasized as the foundation of drawing [3]. Both methods give practitioners a systematic way of drawing that is capable of producing high fidelity and accuracy, but both also have distinct advantages and draw-backs. The sight-size method is structurally rigorous and demands a very controlled environment that is impractical in a large class or studio setting. Its simplicity, and ease of learning, however, make it well suited for small ateliers and academies where a consistent staging and environment is manageable. In contrast, the comparative method allows a greater degree of environmental freedom; for example, students of the method can draw the subject at any distance, and even at different distances between sessions, granted the same viewing angle is maintained. This freedom makes the comparative method ideal for large classroom environments and institutions where controlled spaces are not easily managed. 
The Sight-Size Method of Drawing
Nicholas Beer, in his essay, “The Sight-size Portrait Tradition,” makes the case that the sight-size method can be traced back to painters such as Sargent, Velazquez, and perhaps—Beer suggests—Leonardo. He emphasizes each artist’s use of a common arrangement: placing their easel directly next to their model or subject, and then stepping back some distance to view and compare their drawing to the model [4]. While this does not definitely indicate sight-size drawing [5], it does describe the essential foundation of the method. The sight-size method is, very simply, the process of drawing a subject such that the drawing is the exact dimensions of the subject when viewed from a fixed distance. This method of drawing requires a very rigid environment; the subject, easel, and viewing location must be carefully marked-off and maintained throughout the entire drawing process, as any variation in position will result in changes in scale and perspective that render consistent measurements impossible.  To set-up a sight-size drawing, you must fix a viewing location where you can see your easel and your subject side-by-side, at approximately eye-level. All measurements are taken from this spot, not in front of the easel. Viewing distance determines the scale of the drawing: moving closer to your subject will necessarily increase its scale, and stepping back in space will decrease the viewed size of the subject, and thus the size of the drawing. Once easel, subject, and viewing location have been marked off, you can begin taking initial measurements. From the viewing location, students use string, wooden dowels, or sometimes levels and calipers, to measure first the subject, and then compare to their drawing. Initial marks are made by guesswork onto the paper; by measuring from the viewing location, and comparing between model and paper, you can easily adjust your marks to be consistent with the measurements taken from your model. This process requires a fair amount of ambulation: students move back and forth between viewing distance and their easelssometimes 6 feet or more—drawing lines on their paper, and then going back to compare with their subject. The measurement process itself is a learned skill: students must stand in the same position with their dominant arm extended and locked at the elbow to take a measurement. When using a dowel, or another narrow, rigid tool as your measuring device, you can take distance measurements by aligning the tip of the dowel with a point on the model (the hairline, for instance) and catching a second point with your thumb, like a caliper. If the desired measurement is hairline to chin, the tip of the dowel hovers over the hairline and the thumb slides up the dowel to catch the chin. This distance can then be compared to your drawing, and adjustments can be made as needed, until the measurements on your drawing are equal to those on the model [6].
This video, developed for a life drawing class, demonstrates the first stages of copying a Bargue plate, a standard practice for beginning students of the sight-size method. Charles Bargue was a 19th century artist and instructor who developed a drawing course based on a series of lithographic plates. Importantly, this copying method begins with a 2-dimensional image, thus dramatically simplifying the drawing process, and requires much less stringent arrangements than those described above. Students typically advance from this plate drawing to 3-dimensional subjects, first plaster casts, and then the live model [7].
A distinguishing characteristic of sight-size drawing or painting is an emphasis on the total visual effect, often coalescing for the viewer at a distinct distance [8]. This is a direct consequence of the artist’s viewing, and taking measurements, from a determined distance to both easel and model. The visual material the artist sees is necessarily reduced at a distance, leaving large forms of light, shadow, and hue apparent, as details become harder to distinguish from dominating changes in light or color. Nicholas Beer makes a compelling case that both Henry Raeburn (fig.1) and John Singer Sargent (fig.2) employed some variation of this technique, and that this common approach accounts for the remarkable similarities in their broad handling of paint, a century apart [9]. This method of working, particularly for the beginner, involves a large degree of editing and erasure. Raeburn and Sargent’s paintings conceal the internal construction of their portraits, but student drawings will often show evidence of pentimenti, or erased guidelines [10]. For the conservator, these partially removed marks could appear analogous to accumulated dirt or damage, so an understanding of the drawing and measurement process may help to inform treatment choice, and lend insight to the development and layering of the drawing media.
FIGURE 1 . Henry Raeburn. William Fraser of Reelig (1784–1835), 1801, oil on canvas, 29 1/2 x 24 1/2 in. (74.9 x 62.2 cm), Metropolitan Museum of Art .
Accessed October 1, 2020
FIGURE 2 . John Singer Sargent. Self-portrait, 1906, oil on canvas, 27 1/2 × 20 7/8 in. (69.8 × 53 cm), Galleria degli Uffizi,
Accessed October 1, 2020.

The Comparative Method of Drawing
Comparative measurement allows significantly more freedom for the artist, but can be harder to teach, and learn [11]. It is a versatile method of objective measuring that relies on a ratio of parts, or units, to a whole, rather than fixed-scale rendering. When drawing the figure, a common unit used is the vertical distance of the head, from crown to chin. This vertical distance can be compared to the total vertical length of the body, establishing a ratio; the head-unit may divide 7.5 times (arbitrary, used as an example) into the total vertical length of the standing figure. This ratio allows the artist to construct the figure at any scale, in proportion, simply by structuring a drawing based on this mathematical relationship. If an artist is commissioned to complete a mural on a large wall or building, they can construct their figure proportionally to fill the total height of this area by dividing its distance into 7.5 equal segments. The physical process of measuring in the comparative method is essentially the same as in the sight-size method, simply without the need to stand at a single fixed location to measure. Students use their pencil or wooden dowels, with the same extended arm and locked elbow position to measure areas within the subject. What the artist or student does mathematically with each measurement, however, is different. In the sight-size method, measurements are transferred directly from the subject to the drawing, at a one-to-one scale. In the comparative method, measurements are compared within the subject, and separately, within the drawing. Between drawing and subject, only the ratio of these measurements needs to be consistent; the actual scale of either does not matter.  In a classroom setting, this process of measuring allows much less restricted drawing conditions than sight-size measurement. Students can measure the model or subject at any distance, as ratios remain unchanged by scale or distance. A figure drawn from a distance of 6 feet will have the same head-to-body length proportion when drawn from a distance of 20 feet. The limitations here become very practical: when measuring the distance of the head at 6 feet, you should be able to clearly see the tip of the head, and catch the chin with your thumb using a dowel or pencil. At 20 feet, the size of your thumb or pencil may eclipse large portions of the subject, and any vibration in your hand will cause significant movement over your target measurement, making it very difficult to attain accurate ratios within the model. At a reasonable range, however, comparative measurement gives the artist the obvious advantage of dictating how large their drawing will be, without moving closer, or farther, from the subject, as in the sight-size method. Students begin by measuring the subject. Once they have determined a ratio of parts to the whole, they address their paper. If the total height of their paper is 24 inches, for example, they need only to divide this distance into the necessary number of segments to proportionally construct their subject. Some margin for error should be left at the extremities of the paper, so that the drawing doesn't tangentially intersect the paper’s edges—but within these margins, the artist can work to develop a life-like image without the need to resort to fixed-scale references. The sight-size method is often easier to learn than the comparative method, as the linearity of fixed scale measurements can be less confusing for students to pick up than a scale based on the ratio of parts. Directly transferring measurements from subject to paper in the sight-size method also eliminates a lot of errors that can occur in the comparative method when students measure within their subject, separately from their drawing. The comparative system, though mathematically more convoluted and somewhat less precise, is significantly more flexible, and allows for a more intuitive and responsive working process than the sight-size method [12]. Once the basic concepts of comparative measure have been absorbed, you can use these principles to draw anything with objective proportionand at any scale you choose, with relative freedom of environment and staging. You are not beholden to your distance to the subject, and you can increase or decrease the scale of your drawing at will. 
An example of this flexibility can be seen in Michelangelo’s Studies for the Libyan Sibyl (fig.3). Both the head, left hand, and toes of the figure have been drawn multiple times, and at different sizes. This change in scale strongly suggests Michelangelo used comparative measurements to construct his drawing; if the sight-size method had been used, the artist would need to increase or decrease their distance to the model to effect this scale-change in the image. That scenario seems unlikely given the preparatory nature of the drawing, and Michelangelo’s apparent willingness to work loosely and quickly in the margins—a decision that runs counter to the rigor and exactitude of sight-size measurement. A more likely explanation is that Michelangelo applied an understanding of the ratios of the head or hand, allowing him to expand the scale of his drawing freely. The distance from the lateral corner of the eye to the medial line of the face is, with little variation, proportionally equal to the distance from the brow to the base of the nose. These distances on both heads in Michelangelo’s drawing are consistent, suggesting his reliance on this measurement to construct a proportionally uniform head. The freedom of the comparative method naturally supports the artist’s aims of capturing the details of his model as notes and studies, without the cumbersome labor of staging multiple viewing positions for fixed-scale measurements.
Another instructive example of the comparative method is found in a demonstration drawing by Harold Speed (fig.4). Speed’s drawing is particularly elucidating as his construction lines are intentionally left for us to see. This transparency in process is relatively rare, as many figure studies are ‘cleaned-up’ at the end to hide the construction marks that helped guide the artist’s process. The vertical distance of Speed’s figure happens to divide in half at the navel, offering a broad but essential comparative measurement that allows the artist to begin with any desired height, divide this into halves, and work out from this proportional relationship to smaller and more particular segments of the figure [13].
FIGURE 3 . Michelangelo Buonarroti. Studies for the Libyan Sibyl (recto), ca. 1510-11, red chalk, with small accents of white chalk on paper, 11 3/8 × 8 7/16 in. (28.9 × 21.4 cm), Metropolitan Museum of Art,
Accessed October 1, 2020

Because the comparative system of measurement relies on ratios, and not a fixed scale, mature artists can often work out the ‘math’ of their drawings mentally, skipping the constructive lines and indicators demonstrated in Speed’s drawing. This internalization of the comparative method may account for drawings that appear to have no unit measurements, but still represent a high degree of realism. The absence of construction marks also stands in contrast to the sight-size method, which requires a more direct, trial-and-error approach to establishing a drawing, and may be more likely to express signs of erasure and adjustment. When conservators are faced with drawings that appear to have no visible measurement marks, there is a fair chance the artist has used the comparative method without laying down distinct unit measurements, as seen in Michelangelo’s work above (fig. 3).
The story an artwork tells us is not isolated to either methodology or materials, but is a dialogue between these elements. An artist’s training and technical approach will likely inform their choice of material, and materials necessarily dictate or contour the methods of art production we are capable of developing. It is worth noting that charcoal is a frequent material choice for objective drawing, as it can be applied quickly, and in many cases, removed easily. Understanding the practical demands and consequences of observational life drawing can help conservators assess, analyze, and make judgments about preservation and conservation of artworks. Having a full picture of artists’ working process, as well as the mechanical components of their artwork, gives us a deeper appreciation for the mutual, and sometimes consequential, relationship between methods and materials. Both systems of objective life drawing—given patience and practice—are capable of generating incredibly life-like drawings. These practices, however, aren’t primarily methods or modes of production. Instead, objective drawing is a way to train our eyes to see. The beauty of an objective system of drawing is in its ability to tell us when we’re wrong, to demonstrate inconsistencies that we might not notice as we draw, and to develop in the artist the habits of close scrutiny and visual acuity. Nothing is so useful than to see, for the first or fiftieth time, that our placement of the arm, or leg, or vase, is half a unit too far, or simply not long enough. This surprise causes us to look again, and look closely. Rather than approach objective drawing as a system for inerrancy, these methods help us to see—and experience—the world we live in with deeper clarity. 
FIGURE 4 . Harold Speed. Untitled, in Harold Speed, The Practice and Science of Drawing (Project Gutenberg, 2004), plate 18,
Accessed October 1, 2002

I would like to acknowledge the generous support and advice of Brook Prestowitz and Rebecca Johnston in developing this article.
Photography Credit
Maggie Barkovic (Title Image) and Simeon Youngmann (Video)
[1] Hans-Peter Szameit. The Comparative Method vs. the Sight-size Method. Swedish Academy of Realist Art. 2018. Accessed October 1, 2020
[2] Nicholas Beer. The Sight-Size Portrait Tradition. Charles Cecil Studios. 2009. Accessed October 1, 2020.
[3] Joan Uraneck. Picasso's 'Academic Study of a Cast of a Classical Sculpture' (1893-94) and the Sight-Size Technique. The Burlington Magazine 150, no. 1269 (2008): 826-28. Accessed October 1, 2020.
[4] Nicholas Beer, The Sight-Size Portrait Tradition. [5] Hans-Peter Szameit. The Comparative Method vs. the Sight-size Method. [6] Gerald M. Ackerman. Charles Bargue, with the collaboration of Jean-Léon Gérôme: Drawing Course. (Paris: ACR Edition. 2003), 318-25. [7] Joan Uraneck. Picasso's 'Academic Study of a Cast of a Classical Sculpture' (1893-94) and the Sight-Size Technique. [8] Nicholas Beer, The Sight-Size Portrait Tradition.
[9] Nicholas Beer, The Sight-Size Portrait Tradition. [10] Joan Uraneck. Picasso's 'Academic Study of a Cast of a Classical Sculpture' (1893-94) and the Sight-Size Technique. [11] Hans-Peter Szameit. The Comparative Method vs. the Sight-size Method.
[12] Hans-Peter Szameit. The Comparative Method vs. the Sight-size Method. [13]  Harold Speed. The Practice and Science of Drawing. Project Gutenberg. 2004. Accessed October 1, 2020.