The Art of Drawing a Petal: Visual Microscopy Techniques in the 19th Century

To render the microstructure of petals, 19th-century artists used double magnifying glasses mounted on an adjustable stand, which allowed them to observe the fine textures of the floral epidermis. A medium-hardness graphite pencil was the primary tool for sketching veins and contours, while fine watercolors, applied in successive layers, suggested the transparency and light specific to each species. Pierre-Joseph Redouté, known for his illustrations of roses and lilies, often worked on linen paper, to which he applied a thin layer of gelatin to obtain a perfectly smooth surface.

The technique of color washing was essential: the artist first applied a diluted watercolor to establish the base tone, then added details with fine sable brushes. Each layer had to dry completely before the next, a process that could take entire days for a single illustration. Marianne North, who documented flora from around the world, preferred to work directly in the field, using a pocket magnifying glass and a sketchbook with pressed paper.

Visual Isolation on a White Background: A Scientific Convention

In the botanical treatises of the era, the white background was not an aesthetic choice but a scientific requirement. By eliminating any visual context – landscape, shadows, other plants – the artist forced the viewer to focus exclusively on the morphological details of the specimen. This isolation allowed botanists to accurately compare the shape of petals, the arrangement of stamens, and the texture of leaves across different species.

Augustin Pyramus de Candolle, one of the most influential botanists of the century, insisted that the illustrations in his works be made on white paper, without background shades. In his correspondence with artists, he emphasized that "any spot of color outside the plant is a distraction that can lead to classification errors." This rigor led to the development of a specific graphic style, where fine contours and delicate hatching were the only elements defining the form.

Techniques for Rendering Texture and Light

To suggest the velvety texture of orchid petals or the waxy sheen of blueberry leaves, artists used various hatching and shading techniques. Cross-hatching, done with a graphite pencil, recreated the sensation of plant fiber, while fine watercolor dots, applied with the tip of the brush, imitated the granulation of pollen or nectar. Light was rendered through areas left completely white, where the paper remained exposed, suggesting the reflection of the sun on the petal's surface.

A remarkable example is the illustration of the species Gentiana clusii, created by the Swiss artist Johann Jacob Tschudi. He used a combination of ultramarine blue watercolor and black ink to render the intense hues of the petals, while simultaneously leaving white areas to suggest the light penetrating the corolla. The drawing was included in the treatise Flora Alpium and became a reference for identifying the species for decades.

Collaboration Between Artists and Botanists

The relationship between illustrators and scientists was one of interdependence. Botanists provided fresh or pressed specimens, along with detailed notes on the exact color of the petals, the flower's scent, and the texture of the leaves – details that were lost in the drying process. Artists, in turn, brought a deep understanding of light and composition, transforming scientific observations into images that could be reproduced in hundreds of copies through lithography.

Marianne North, for example, collaborated with botanist Joseph Dalton Hooker at the Royal Botanic Gardens, Kew. She created over 800 illustrations of plants from India, Australia, and South America, each accompanied by notes on habitat and flowering period. Her works, displayed today in the Marianne North Gallery at Kew, are considered scientific documents of primary importance.