Decision tree for the preliminary investigation and characterization of plating by visual examination.
Full Text
PRELIMINARY INVESTIGATION OF PLATING BY VISUAL
EXAMINATION
(use a magnifying lens and good raking light; see text
for details of the plating techniques mentioned)
Identify the color of the body metal of the sculpture. Look for metallic areas of a different color than the body metal and/or bright metal within corrosion layers.
Note: There may be more than one type of plating present. Use elemental analysis if available (e.g., XRF or spot tests) to identify the plating material and the sculpture metal (see table 10).
If there is plating inside a hollow sculpture: suspect electroplating (but small splashes or runs may be amalgam plating if mercury is detected, or fusion plating if it has a cast structure and no mercury).
If there is evidence of rivets, grooves, or other fixings: suspect mechanical foil gilding. Look for fragments of foil, and/or try X-radiography.
If there is scoring on the sculpture: suggests close plating with silver foil or foils added as local repairs.
If there is a gesso coating on the sculpture: look for leaf gilding.
If the plating has straight edges and/or square shapes: leaf gilding likely. Undertake elemental analysis: Is it gold, or copper + zinc (Dutch leaf)? Silver or tin?
If the plating is flaking off: indicative of deterioration of adhesive used for leaf gilding.
If the plating is blistering: a problem of electroplating, but also caused by corrosion under most plating.
If the plating has a granular texture: suspect paint; also look for brushstrokes, drips, etc. (see I.8).
If there are metal runs and drips: suspect amalgam plating (check for mercury) or fusion plating.
If only selected areas are plated: leaf, paint, amalgam, or electroplating (using a masking material) are possible.
If a gilding layer is worn on high points but not flaking: suggests amalgam (test for mercury) or electroplating (look for blistering).
If gilding is well bonded but thin: suggests amalgam (test for mercury; if none, diffusion bonding or electroplating are possible).
The next stage of investigation would be to take a sample that provides a cross section of the plating in relation to the substrate metal. See II.6.