Structural Sketch of an Office Chair

Drawing a structural sketch of an office chair involves four stages: contour positioning, sectional depiction, light and shadow shaping, and texture differentiation. The specific steps are as follows:

I. Contour Positioning and Structural Decomposition

1. Basic Positioning: Lightly draw a horizontal straight line on the drawing paper as a ground reference. By comparing the straight line with the vertical proportions of the chair, quickly determine the overall height of the chair and the positions of its various parts (such as the relative heights of the seat, backrest, and base).
2. Sectional Outlining:
   • Leather Seat: Use smooth curves to depict the edges of the seat, emphasizing its soft texture. The internal contour lines should naturally connect with the edge curves to avoid abrupt turns.
   • Metal Base: First, draw the left and right support legs, then add the three middle support legs. Pay attention to the perspective relationship of near-large and far-small to ensure the accurate connection positions of the five support legs with the wheels.
   • Backrest and Armrests: Depending on the type of chair (such as with or without armrests), use straight or curved lines to position the inclination angle of the backrest. The armrests should be parallel to the edges of the seat, following the principle of near-large and far-small.

II. Light and Shadow Shaping and Volume Establishment

1. Unified Backlight Surface: Use a 5B soft pencil to uniformly coat the backlight surfaces of the seat and base, determining the darkest areas of the drawing and laying the foundation for subsequent layer differentiation.
2. Dark Part Intensification:
   • Leather Parts: Use a 7B pencil to deepen the dark parts at the folds and joints of the seat. The connection areas of the wheels and support legs should be depicted with the same brushstrokes to convey a sense of weight.
   • Dark Surface Transition: The dark parts of the leather should be represented with gradient hatching to show soft turns. The gray surfaces should be differentiated from the bright surfaces with subtle hatching, and reflective strips should be reserved at the joints to enhance the three-dimensional effect.

III. Texture Intensification and Detail Correction

1. Leather Texture:
   • Use a 6B pencil to refine the joints of the various layers of leather on the seat, representing the three-dimensional effect of the splicing with white reflective strips.
   • Use a paper stump to smudge the dark and gray surfaces, blending the hatching marks while retaining the highlight areas to give the leather a natural luster.
2. Metal Texture:
   • Determine the range of the dark parts according to the light source, intensify the contrast between the gray and dark surfaces to highlight the reflective characteristics of the metal.
   • Lightly dot the highlight areas with a sharpened 6B pencil, keeping them small and sharp to form a texture contrast with the highlights of the leather.
3. Overall Adjustment: Use a 6B pencil to deepen the dark parts of the leather and the gray surfaces of the metal, restoring the black, white, and gray layers to ensure a clear hierarchy of the main and secondary elements in the drawing.

IV. Tool and Technique Points

1. Pencil Selection: Use a 5B pencil for laying the base colors, a 7B pencil for intensifying the dark parts, and a 6B pencil for refining the textures. Soft pencils are easy to color and suitable for representing soft transitions.
2. Paper Stump Application: Smudging can unify the tones, but subsequent contrast should be added with a pencil to prevent the drawing from becoming dull.
3. Perspective Control: The armrests and support legs should follow the principle of near-large and far-small to ensure accurate spatial perception of the structure; the chair legs and backrest belong to the same vertical plane space, and the perspective relationship should be understood from a spatial perspective.