copper resinate

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It is a transparent green glaze used between the 15th and 17th centuries.

Manufacturer/ product code: Kremer / 12200
Chemical Description: copper(II)-acetate-1-hydrate (C4H6CuO4 · H2O) cooked with colophony in white spirit.
Color: green
Color Index: n/a
More info: Kremer

Copper resinate is a historically significant green pigment, widely used in European painting from the late Middle Ages through the Renaissance, particularly in oil technique. Unlike mineral greens such as malachite or verdigris, copper resinate is an organic–inorganic hybrid material, produced by dissolving a copper salt—most commonly copper acetate—into a resinous medium derived from pine resin or Venice turpentine. The resulting copper–resin complex yields a highly transparent green, ideally suited for glazing rather than opaque paint layers.

Artists valued copper resinate for its intense saturation and depth, especially in the rendering of foliage, textiles, and shadowed areas. Applied over lighter underlayers, it allowed painters to build luminous greens with subtle tonal modulation, an effect difficult to achieve with body colors alone. For this reason, copper resinate frequently appears as thin, translucent layers in oil paintings of the 15th and 16th centuries, often in combination with azurite, lead white, or verdigris.

Despite its aesthetic appeal, copper resinate is chemically unstable. Over time, interactions between copper ions, resin, and oil promote oxidation and polymer breakdown, leading to progressive darkening and browning. Many areas that were originally bright green now appear dull, olive, or nearly black. This degradation has significant implications for both the visual interpretation and conservation of historical paintings.

From an analytical perspective, copper resinate presents notable challenges. XRF spectroscopy readily detects copper but cannot distinguish it from other copper-based pigments. Identification therefore relies on a multi-analytical approach, including infrared imaging, microscopic examination of paint stratigraphy, and molecular techniques such as FTIR or GC-MS. Understanding the presence and behavior of copper resinate is essential for accurate material interpretation and informed conservation strategies.