Scientific Illustration

Halftone Illustration with Plastic Pencils on Drafting Film: A Vanishing Art 

By Alice Tangerini 
Originally appeared in The Botanical Artist, Volume 14, Issue 3


The use of halftone or continuous tone media for botanical illustration has usually been relegated to preliminary pencil sketches or illustrating bulky subjects as fruit or seeds. Generally spending time filling in flat leaves with tone has not been considered expedient and pen and ink was the preferred media. I found a case to use this pencil technique to illustrate species of Asteraceae where leaves were sometimes bi-colored (upper and lower surfaces) and the heads in the inflorescences retained their three dimensional aspect even on pressed specimens along with variations in color in the involucral bracts. Graphite seemed like the optimum media for this case and plastic pencils that were formulated to adhere to drafting film appeared to be the best tools. 

When I was first asked to write about this technique I realized too late that the plastic pencils that were readily available up to the year 2000 have been discontinued by many of the companies that made them. My own resources for these pencils were always in the drawers in my dental supply cabinet where I squirreled away a surplus of tools. So I may be giving a summary of a past art technique, however, diligent searching may give you some wonderful tools. 

My introduction to plastic pencils on drafting film came when I was asked to illustrate plants to continue a series of drawings begun by Jack Schroeder, a freelance illustrator at the National Museum of Natural History in Washington, DC. Back in the early 1970’s Jack developed the technique of plastic pencils on drafting film,originally for fish illustration where the differentiating patterns and scales required a full tonal range from black to white. He was then contracted by two botanists in my department to illustrate plants in the family Asteraceae and he decided to continue this technique. 

I was familiar with drafting film, also known as polyester or polypropylene or polyethylene. All of these served as drawing surfaces that accept graphite and ink although the variation in the surface textures influence the application of the media greatly. Drafting films are for the most part archival and withstand extreme heat and resist water. I find that the Grafix brand Duralar drafting film accepts the pencil with a nice tonal depth and is also erasable. 

The process for drawing with plastic pencils begins with an underlying sketch or a photocopy of the plant as the base. Many of my base drawings are actually layers of individual drawings on transparent bases (translucent paper, films, etc.). I can composite the elements into a single, pleasing/useful presentation. The drafting film, which is translucent, is placed over the composite sketch and the plastic pencil is used to trace the sketch onto the film. 

Plastic leads are formulated for use on drafting film. they come in grades with the softest leads producing an intense black. They bond cleanly to film without smudging and can be erased, although with enough buildup of graphite it becomes more difficult. Plastic leads are made from a combination of graphite and plastic polymer. A plastic pencil is waxier in feel than regular graphite and does not smudge so lines stay in place. Always cover areas of the film not being drawn on to protect it from hand oils or wear cotton gloves. 

Beginning with a medium soft (in the same range as an HB) lead, trace the sketch outline onto the film with delicate pressure, as heavy pressure can dent the film. Once all outlines and information from the sketch are transferred the sketch may be removed and the film backed with very smooth Bristol board. A textured surface backing board can transfer to the drawing in the shading. 

I next apply darker areas with one of the softest leads (similar to a 2B/3B) with light pressure. I hold the pencil at an oblique angle, almost horizontal to the film surface, for this shading. I then work up large areas of middle grays as in the leaves with a mid-range soft lead. 

Generally I work in the direction of leaf contours - from the mid-vein outward toward the margin. Once a direction of shading is established it should be continued so as not to create shifts in stroke direction. Avoid cross-hatched strokes as this can be unsettling to view and interfere with a buildup of the grays. As in regular graphite, it is difficult to work a soft lead over a harder grade of lead. 

Areas of highlights can be erased later with a vinyl eraser by hand or with electric eraser. Don’t allow an electric eraser to sit too long in one spot. It may wear off the film coating. Last, I use the harder grade leads to even out the tones and for details requiring fine lines. Vestiture (surface details and textures) may be added with a darker lead, with scratching out the grays with an Xacto knife for lighter details, or even adding a mixed media touch with ink. Ink may look too hard edged so I always experiment on a sample. 

This technique can produce lovely patterned leaves and seeds. I have done many plates of achenes this way making full use of dense black on the seed coat. 

Jack Schroeder had a slightly different approach to this technique. His theory on successful illustration was associated with having a couple of martinis while drawing! His drawings were highly crafted and polished and he was able to achieve a smooth tone over a large leaf without showing pencil lines. He says, “the trick is to keep an even pressure on the pencil, and to keep the lines very close and all the same weight the first time over the area. Usually a second pass with a sharp pencil to fill in between the first lines will give you an even tone.” I am more comfortable having pencil lines following the contours of the subject so if any lines do show they are relational to the surface. Either technique produces rich tonal renderings and I hope you have an opportunity to try it. 

Author’s note on supplies: When I began using these pencils they were readily available. Now, they can be found online. Current film types include Graphix Duralar and Azon, who makes Herculene and Dietzgen. 

Editor’s Note: Sanford’s Pentel line makes leads for film in 3 sizes .5, .7, and .9 mm. Each comes in soft, medium and hard. They are used in standard lead holders. Loading the pencil is interesting, as the poly leads are very flexible! I found my leads at a local art store in Denver, but also found listings for Pentel leads on several office supply, drafting and arts websites. These leads are a very sensuous medium, laying down a smooth, toothless tonal value. Creamy. I think I’ll be trying more of this!  

  • Sampera coriacea V.Funk & H. Robinson is a new species in the Asteraceae and is named in honor of the Director of the National Museum of Natural History, Cristian Samper.
  • The illustration of the Heliantheae achenes was published in Flora of Ecuador: 77(1): Compositae-Heliantheae. 2006.
  • This species in the Asteraceae, Erato costaricensis E.Moran & V.A.Funk, was published in Systematic Botany: 31(3): 2006.