Transparent Liquid Colors: “Not Just For Ornament” by Joan Irving
In the 18th century, stationers' catalogues began to list liquid transparent colours. Are these different from regular watercolours? In fact, they are a fundamentally different product, formulated for their transparency for use on maps and plans so as not to obliterate key information.
Previous to this time, watercolour paints were used for tinting prints, maps and drawings. Pigments were purchased dry, or mixed with gum arabic in shells acting as pans. These evolved into dry cakes and then tubes of paste paints. The colourwoman Elizabeth Emerton sold shell paints in 1728. Liquid watercolours transitioned from house paint to the studio. Wallpaper stainers' brushes were seen in trade cards, used to create the even washes needed for large areas.
Transparent colours were described as “chemical colours for maps, plans & architecture” and were aimed at specialist uses including drafting, surveying, and architectural drawing. Manuals described how to prepare these colours. In the 1780s, prepared transparent liquid colours began to be imported to North America.
(1672) discusses the manufacture of general colours for “limning” or washing maps - these colours include mineral pigments such as vermilion, red lead, red ochre, masticot, orpiment, ultramarine, bice, verditer, terre-verte, and verdigris.
In Laurence’s Young Surveyors’ Guide
(1716), the transparent colours used in washing maps are not the same as watercolours.
In looking at samples, we can examine the transparence or opacity which is affected by:
- Particle size
- Refractive index (mineral pigments have a higher RI than organic ones)
- Agglomeration (Dossey says mix with additives to reduce)
- Additives (Ox gall, honey, isinglass, alum)
Robert Boyle’s Treatise on Colours (1823) gives directions on making transparent liquids. Joan Irving made red transparent liquids using brazilwood (with steeped shavings), gamboge, verdigris, and cochineal. Potash alum was obtained from Kremer Pigments. The pH can be altered with soap lees or vinegar. The liquids are then stored in bottles for use.
In researching, be aware that modern watercolour cakes have small particles compared to historic watercolour cakes, and are therefore not suitable for direct comparison. Look microscopically at historic samples and new reconstruction samples - for instance, old carmine (cochineal) samples have small particles, and new samples appear smooth. In some historical objects with professional colour like maps and atlases, you can see both liquid colour in the washes and solid (shell) colour in the border. Debris/particulates bound in with the medium can be seen on historic objects. When reconstruction liquid preparations were strained through a cheesecloth without being allowed to sit, the debris was able to be seen.
Cakes, used until around 1860, included many mineral colours, the wash on paper appears dappled not stained, in medium-dark washes many finely divided, ground pigment particles of consistent size are seen, and pale washes appear clean with no visible debris.
Transparent liquids are mostly vegetable colours, the paper appears dyed or stained, in medium-dark washes there is little visible pigment and it is scattered, and pale washes have visible scattered very small debris.
Transparent liquids changed through the 19th century, with semitransparent colours appearing such as Prussian blue, and technicians siphoning off the smallest particle sizes.
Future research possibilities include using HPLC (high performance liquid chromatography) to “sample the unsampleable”, and using tiny agarose plugs to wick up liquid.
- Who used transparent colours? Professionals (in other words, not amateur artists).
- Can we tell if transparent colours were used? Sometimes - by looking at the density and presence/absence of debris.
- How are they different? They are vegetable tisanes rather than paints.
- Why should we care? Out of connoiseurship, and for better informed conservation treatment and preventive care.
One of the last points made in this presentation was that transparent liquid colours are usually quite fugitive and we really don’t expect to see them. This point made learning about the historical production and application of these colours even more intriguing, since the traces of their use might be so easily overlooked.
Here are some of the books mentioned in the presentation:
Polygraphice, or, The art of drawing, engraving, etching, limning, painting, washing, varnishing, colouring, and dying
- William Salmon (1672)The Young Surveyor's Guide
- Edward Laurence (1716)The Handmaid to the Arts
- Robert Dossie (1764)A Treatise on the Construction of Maps
- Alexander Jamieson (1814) The painter's companion, or a treatise on colours
- Robert Boyle (1823)The art of drawing in its various branches
- Thomas Smith (1827)
Julie Niven, Archives Conservator
Mills Memorial Library, McMaster University, Hamilton, Ontario
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