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“The best preparation of smalt”?
A lasting honey coating
On Smalt ParticleS

Portrait of Technical Art Historian Paul van Laar, colourized in blue

 PAUL J.C. VAN LAAR*, DOMINIQUE M.E. THIES-WEESIE, THIJS HAGENDIJK, MAARTJE STOLS-WITLOX, GERT JAN VROEGE

1. Background: Smalt Experimentation

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  • Smalt is a finely ground blue-coloured glass that was used as a painter's pigment

  • Artists were aware that smalt was difficult to handle and prone to discolouration when used in oil paint​

  • Historic sources reveal experimentation among artists:​

    • Alternative binding media.​

    • No binding media ("strewing smalt")

    • Specific pigment mixtures (e.g. lead white)

    • Alternative natural grinding media

Rublev powdered Royal Smalt
A glass muller grinding the blue pigment smalt in oil
Symbol of honey

2. Eikelenberg's (1663-1738) ervarenis

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  • Unpublished Dutch manuscript on the art of painting​

  • "Ervarenissen" that describe experiments in his studio

  • 1701: grinds smalt with "good, white honey"

Portrait of Simon Eikelenberg, re-colourized in blue.

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3. Other peculiar grinding media

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  • Pseudo-Savonarola, ~1535: Smalt and milk​

  • MS2265 (Casanatense, Roma), 14th century: ismalto and egg

  • For other pigments: white wine, vinegar, urine etc.

Milk symbol
Egg symbol

4. Reconstructing Eikelenberg's Experiment

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  • Eikelenberg describes the following:

    • Grinding for upwards of an hour ("ruym een uur")

    • Washing the pigment several times to remove the honey

  • He remarks that "this is the best preparation of smalt that [he has] known until now."

  • Reconstructions were compared with a control group ground with water

Grinding

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  • In honey or water

  • 2 variations: 8 or 60 min

Washing

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  • Repeated 3 times

  • 300 mL, control with 2 L

Final Pigment​

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  • Dried and analysed

Schematic image of washing the blue pigment smalt in water
Schematic image of blue smalt pigment particles with a coating of honey around them
Schematic image of a muller grinding the blue pigment smalt in honey

MAIN FINDING

Despite extensive washing, a lasting honey coating is detected on the smalt particles

TEM micrograph of smalt particles with a honey coating. Sample treated with Uranyl Acetate

5. Effects

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  • The coating reduces agglomeration during washing

  • This facilitates the removal of the smallest non-colouring pigment particles









     

  • The isoelectric point (IEP) of the pigment changes, revealing alterations in the surface properties of the smalt particles.

Inverted light micrographs at 40x magnification of the particles removed during washing.
Smalt ground with honey (left), or with water (right).  

Micrograph. Microscopy of aggregated blue smalt pigment particles in a solution.
Micrograph. Microscopy of aggregated blue smalt pigment particles in a solution.
Zeta Potential of various blue smalt pigments
TEM micrograph of smalt particles with a honey coating. Sample treated with Uranyl Acetate

6. Conclusion, Context & Future Research

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  • Analysis examining which component in the honey is responsible for coating the smalt particles proved inconclusive so far. Further research is required.

  • Eikelenberg's ervarenis reveals that artists not only manipulate binding media, as a growing body of research is showing, but also sought to alter pigment properties through various treatment and processing techniques. The experimental attitude of painters and writers towards smalt should be studied in the wider vein of paint property manipulation.

  • The technical art historical implications of the honey coating are the topic of future research:

    • It likely ​influences the rheological behaviour of the pigment particles in oil paint systems. Preliminary tests suggest a lower viscosity and better flow for paints with honey-coated smalt particles.​

    • As smalt degrades through the leaching of components from its glassy core, the coating could play a role in the common discolouration mechanism.

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