Classification

Contrary to the line taken in the previous guidelines, this publication does not assume that treatment is useful for all (leather) bookbindings. We now suggest treating only those bindings which qualify on the basis of both visible damage and the measured pH value. The pH limits have been so determined as to restrict deacidification and buffering to the urgent cases. It will, however, always be considered useful to remove dirt and dust from bindings.
This chapter describes how to assign leather and parchment bookbindings to various damage categories on the basis of visible damage and pH value and provides a step-by-step guide to the most suitable conservation treatment for the type of damage concerned. For practical reasons each damage category is designated by a different colour. When a binding has been assigned to a particular damage category, a strip of acid-free paper with the appropriate coloured sticker is placed inside the book. These strips can also be used for treatment notes specific to the bookbinding in question, such as indication of a local treatment (spine, joint) and/or the fat percentage (5 %, 10 %) of the emulsion or dressing to be used. In principle treatment consists of one or more steps that must always be carried out in the following sequence: cleaning, deacidification, buffering, conditioning, treating with emulsions or dressings, and impregnating.
Chapters 5 and 6 will deal in more detail with the recommended procedures and the necessary formulas required for the treatments discussed.
The procedure for measuring the pH value of leather and parchment will be described in chapter 7 together with a number of other analytical tests.
The damage categories dealt with in this chapter (apart from mere dust and dirt on the bookbindings) involve physico-mechanical and chemical forms of damage that are likely to be found in most of the common kinds of leather and parchment bookbindings.
A number of special damage categories - damage to specific kinds of leather (alum-tawed and leather with pigmented finishes), leather and parchment overtreated with fat, and biological damage - will be discussed in chapter 5 together with a description of the relevant treatment procedure and formula preparation.

Leather


There are 4 damage categories for leather: white, yellow, blue, and red.

Damage category: white

Description
Leather with a contaminated surface but no other forms of physico-mechanical and/or chemical damage.

Characteristics Loose and/or fixed dirt and dust.

Treatment

  • Cleaning

Damage category: yellow

Description
Leather bookbindings with physico-mechanical damage where the leather has a pH value greater than 3.0.

Characteristics
Cracks, loosened grain, damaged joints.

Treatment

  • Cleaning
  • Buffering, if pH <4.0
  • Conditioning
  • Treatment with emulsion

Explanation

  1. Emulsion is permissible for leather without chemical damage. Leather with physico-mechanical damage, but a pH value below 3.0 belongs in the next category (blue).
  2. Depending on the seriousness of the physico-mechanical damage, an emulsion of 5% or 10% fat is used. The emulsion can be applied locally, if so desired.

Damage category: blue

Description
Leather bookbindings with chemical damage.

Characteristics
Cracks, loosened grain, pulverised grain; local, varying degrees of discoloration (in instances of leather marbling or other leather decoration techniques).

Treatment

  • Cleaning, removal of loose dust and dirt only
  • Deacidification, if pH value <3.0
  • Buffering, if pH value <4.0
  • Conditioning
  • Treatment with leather dressing

Explanation

  1. This damage category includes leather bindings which, though exhibiting physico-mechanical damage characteristics, should be regarded as having chemical damage because of their low pH value (<3.0).
  2. Due to the vulnerability of chemically damaged leather, only loose dirt and dust can be removed.
  3. Only leather with a pH value below 3.0 needs both deacidification and buffering; when the pH value is between 3.0 and 4.0 only buffering is necessary.
  4. Leather with chemical damage is treated with leather dressing, because an emulsion (water!) may cause additional damage.
  5. Depending on the seriousness of the chemical damage a leather dressing with 5% or 10% fat is applied; the leather dressing may be applied locally, if so desired; if necessary the joints and spine may be treated with an additional lanolin dressing.

Damage category: red

Description Leather bookbindings with serious chemical damage.

Characteristics Leather completely pulverised and disintegrated.

Treatment

  • Cleaning, removal of loose dust and dirt only
  • Deacidification, if pH value <3.0
  • Buffering if pH value <4.0
  • Conditioning
  • Treatment with special leather dressing to prepare for impregnation
  • Impregnation

Parchment

For parchment we can distinguish 2 damage categories: white and green.

Damage category: white

Description
Parchment bookbindings with a soiled surface, but no other forms of chemical and/or physico-mechanical damage.

Characteristics
Loose and/or fixed dust and dirt.

Treatment

  • Cleaning, removal of loose dust and dirt only.

Explanation
Fixed dirt and dust should only be removed if there are particular reasons for doing so.


Damage category: green

Description
Parchment bookbindings with physico-mechanical or chemical damage.

Characteristics
Distortions, greyish discolorations (especially on the spine), tearing, splitting and/or crumbling of the parchment, damaged joints.

Treatment

  • Cleaning, removal of loose dust and dirt only
  • Deacidification, if pH value <5.0
  • Buffering if pH value <6.0
  • Conditioning
  • Treatment with parchment dressing

Explanation

  1. As the difference between physico-mechanical and chemical damage of parchment is not always clear and the treatment of both damage categories is basically the same, these forms of deterioration have been placed in a single damage category.
  2. Cleaning of deteriorated parchment should be limited to the removal of loose dust and dirt.
  3. The combination of deacidification and buffering is only necessary for parchment with a pH value lower than 5.0; if the pH value is between 5.0 and 6.0 buffering will be sufficient.