Deacidification vs bleaching. Watercolour conservation

CASTELLANOCATALÀ

  • Owner: Private collection.
  • Artwork: Watercolour drawing by Rafael Estrany.
  • Date: 20th century.
  • Damages: Foxing stains.
  • Conservation treatment: Wet cleaning and deacidification with calcium hydroxide.

Before we decide to bleach with the goal of removing foxing stains, we should assess whether the beneffits of a deacidification give an acceptable result or not. Deacidification, unlike chemical bleach, is good for the preservation of the document because it provides an alkaline buffer. Bleaching treatments, either with sodium hypochlorite (bleach), hydrogen peroxide or other products, carry RedOx reactions which might weaken cellulose fibers and may involve a revival of the spots we intended to remove. The goal of deacidification is not to remove stains, but it may be a desired consequence of it, at a certain degree.

fugitivity test

fugitivity test on inks  previous to washing.

Aquarel·la Estrany

Watercolour during wet cleaning.

 

Aquarel·la Estrany

Left: Detail of foxing stains before treatment. Right: after washing and deacidification.

Watercolour restoration Estrany

Watercolour after (left half) and after the conservation (right half). Digital photomerge with the two original images.

 

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Why deacidify if it is hardly visible?Deacidification / Bleaching / Light Bleaching Foxing