Contract for the services of a well equipped scientific analytical laboratory. Determine the exact composition of the polychromed gesso piece undergoing restoration. Place the object under full ultraviolet illumination. Photograph the front and back of the artifact to see previous restorations and weaknesses in the gesso. Conduct thorough mineralogical, chemical and morphological analyses of the polychrome pigments using high-powered optical and electronic microscopy, infrared spectroscopy and an energy dispersion system, or EDS.
Restore the polychromed gesso artifact to its original condition by reconstructing the composition of the gesso, glue sizing and polychrome pigments. Prepare the compounds following formulae resulting from the analyses. Mix gesso based on the same clay or chalk type as the original. Recreate new pigments with their original binding medium of oil or tempera. Use the same-pigment minerals to match the original polychrome hues.
Collect all detached fragments of the polychrome gesso for reattachment. Clean the entire artifact with soft-bristle Japanese brushes. Use ultra-thin needles to inject the artifact with acrylic emulsion adhesive to firm up and consolidate the gesso. Dilute the emulsion 20 percent with ethyl alcohol. Keep water from contacting the soluble pigment and gesso layers. Take advantage off the humidification effects of the emulsion solution injections to reshape warped or dented areas of the gesso. Push out the blemishes with polyurethane foam spacers.
Removed decayed materials from past restorations that were detected by the analyses. Repair surface tears with acrylic emulsion adhesive diluted with 30 percent ethyl alcohol. Brush the emulsion onto the torn edges with a paint brush. Reinforce worn areas with overlapping sheets of thin Japanese paper soaked in the emulsion solution. Fill in openings and fissures with the reconstructed gesso.
Clean the polychrome paint with a Japanese manila paper solution composed of equal parts ethyl alcohol and acetone. Secure loose areas of the polychrome with a cellulose ether consolident diluted 6 percent with the alcohol-acetone solution. Reattach the loose polychrome gesso fragments using emulsion adhesive solution diluted 20 percent with ethyl alcohol. Inpaint the worn spots in the polychrome colors with glazes of the reconstructed paints.