We are surrounded by so much paper and card that it is easy to forget just how complex it is. There are many varieties and grades of paper materials, and whilst it is fairly easy to spot
varieties, it is far more difficult to spot
grades. It needs to be understood that most paper and card is manufactured for a specific purpose, so that whilst
corn-flake packet may look smart it is clearly not something destined for
archives. It is made to look good, but only needs a limited life span. It is also much cheaper to manufacture than high grade card.
Paper can be made from an almost endless variety of cellulose based material which will include many woods, cottons and grasses or which papyrus is an example and from where we get
word ‘paper’. Many of these are very specialized, but
preponderance of paper making has been from soft wood and cotton or rags, with
bulk being wood based.
Paper from Wood. In order to make wood into paper it needs to be broken down into fine strands. Firstly by powerful machinery and then boiled with strong alkalies such as caustic soda, until a fine pulp of cellulose fibres is produced. It is from this pulp that
final product is made, relying on
bonding together of
cellulose into layers. That, in a very small nutshell, is
essence of paper making from wood. However,
reality is rather more complicated. In order to give us our white paper and card
makers will add bleach and other materials such as china clay and additional chemicals.
An further problem with wood is that it contains a material that is not cellulose. Something called Lignin. This is essential for
tree since it holds
cellulose fibres together, but if it is incorporated into
manufactured paper it presents archivists with a problem. Lignin eventually breaks down and releases acid products into
paper. This will weaken
bond between
cellulose fibres and
paper will become brittle and look rather brown and careworn. We have all seen this in old newspapers and cheap paperback books. It has been estimated that most paper back books will have a life of not greater than fifty years. Not what we need for our archives.
Since
lignin can be removed from
paper pulp during manufacture
obvious question is ‘why is it left in
paper?’ The answer lies in
fact that lignin makes up a considerable part of
tree. By leaving
lignin in
pulp a papermaker can increase his paper yield from a tree to some 95%. Removing it means a yield of only 35%. It is clearly uneconomic to remove
lignin for many paper and card applications.