Conservation Science

114 Chapter 5

there was evidence that in highly polluted atmospheres the acidic environment
suppresses oxidative reactions.
It can be concluded that chemical degradation of vegetable-tanned leather
will occur in both polluted and unpolluted environments, and that both oxida-
tive and hydrolytic reactions are always involved. The preponderant mechan-
ism will depend on the exact conditions to which the leather is subjected.
It should also be noted that the rate of decay of leathers exposed to the
mainly hydrolytic effects of acidic urban atmospheres is much greater
than the oxidative deterioration found with leathers held in cleaner rural
surroundings.
Research has been carried out to determine the mechanism of deterioration
of parchments. This has shown a very similar combination of oxidative and
hydrolytic attack.
Further investigations, funded by the European Commission CRAFT pro-
gramme, have also been undertaken to develop a leather with both the resist-
ance to acidic atmospheric attack exhibited by mineral tanned leathers and the
physical characteristics of vegetable-tanned skins demanded by book binders
and other leather workers. As a result of this work, leathers with these proper-
ties are now available commercially.

α amino adipic acid

O O

H

H N H

H H

H

H

H OH

N N

H

H

H

H

O

O

H

H N H

H H

H

O

OH

glutamic acid

+

+

urea

NH 3

ammonia

NH

O H

H

H N H

H H

H

H

H

H

H

lysine

• 
  

O

O

H

H N H

H H

H

H

H

H

NH 3

allysine

+

*

arginine

O

H

H N H

H H

H

N

H

H

NH

H

H

N

H

• 
  

ornithine

O

H

H N H

H H

H

H

H

N

H

* H

Figure 10Possible oxidative mechanisms for the production of acidic side groups from
basic amino acid residues. Asterisk * indicates site of oxidative attack