But now that you bring the subject up, I think the list would be very
interested next in learning some of the plusses and minuses of the 3
different types of paper. (Anyway, I would.)
On Tue, 27 Aug 1996, Bas van Velzen wrote:
> mono-layer: tear the paper cross grain- no layers will become visible
> multi-layer couched:tear in same way- layers will be visible (up to three)
> multi-layer glued: burn corner of paper- layers will be visible (as ash)
> and will have separated, fanned out -couched papers will not show separated
> layers after burning-
As you will remember I always had hesitations with multi-layered
objects. Especially when they are supposedly single property items (such as
CD's, photos etc.) The fact that they have more than one layer means that
the layers interact with each other. This goes for paper too! Here I am
talking about machine made paper, handmade paper has all the described
properties but not so prominent and often hardly distinguishable.
Couched paper is most times made pressing the felt sides* of two
paper rolls of two paper machines together when the paper is just made (the
water content of the paper will be between 10 and 8%) in this way the paper
fibers can still intertwine a little and establish a bond. This is done to
give the paper the same (printing) characteristics on both sides. On
wetting such sheets in a water bath air bubbles can form between the two
layers. The bond between the layers is not so strong as to prevent this.
When two different papers are couched together the paper will have more
problems since the layers will act differently on wetting. The paper will
be fairly easy to flatten after wetting.
Glued papers are more stiff than couched papers and since this bond
is most times stronger air bubbles will not easily form on wetting. Glued
papers will have more problems in lying flat when dry because the glues
contain water. The paper rolls being glued together will swell on one side
and develop stresses on drying. The papermaker will try to avoid these
stresses by carefully conditioning the paper before and after glueing.
Glued papers can also be made using sheets. These will have the machine
directions changed with each layer thus more or less eliminating stresses.
Wetting glued papers in a water bath will release the stresses in the
paper, it will be very difficult to flatten the paper afterwards.
In general mono layer papers are the most easy to control, although
the two sides are slightly different the overall stresses are lesser in
these papers. The heavier the paper can be made in one layer the less these
differences will be noticeable. A heavy paper will be about 180 grs/m2.
Above this weight it will soon be called carton and above about 400 grs
board. Cartons and board will almost always have more than one layer.
Handmade papers, when well made, will have less stresses, less
direction and less differences between sieve and felt side. Also a fresh
made paper will be more difficult to control than matured paper, the drying
stresses are still present in the paper. Remember that in machine made
papers the fibers are totally saturated with water when poured on the sieve
and then dried in a matter of minutes to 3% water content. This stresses
the fibers very much. When I buy paper I will keep it for over a year to
mature it. Keep your paper well protected from light and dust and keep it
flat. In cases where the paper is not flat keep it under just enough weight
to have it flat. After some time you will see the paper will keep flat even
after taking away the board and weight. Heavy cockled papers cannot be
flattened when the air is dry (under 40% RH), wait for the wetter season.
For those who have the time and energy to read a little more on this
subject:
Hunter, Dard
Papermaking, the history and technique of an ancient craft
New York 1947, 19?? - Dover publications
ISBN 0-486-23619-6
Heller, Jules
Papermaking, the white art
New York 1978 - Watson-Guptill publications
ISBN 0-8230-3895-5
Saltman, David
Paper basics: forestry, manufacture, selection, purchasing, mathematics and
metrics, recycling
New York 1978, 1991 - Krieger publishing company, Malabar, Florida
ISBN 0-89464-569-2
Turner, Silvie
Which? paper
New York 1994 - Lyons & Burford
ISBN 1-55821-312-0
* paper has two sides: the sieve side where the paper lies on the sieve
when being formed contains more smaller fibres. This means that when wetted
the sieve side will swell more and is bigger in this situation. The sieve
side can be recognized in raking light: look for a sieve structure. Also in
coloured papers the sieve side is darker: pigments will sink in the paper
due to gravity and dyes will adhere more easily to the short and relative
broad fibers.
The felt side is pressed together with the couching roll (which is
made of felt) and is therefore more compressed and smoother. Sometimes a
structure is pressed in the paper on this side with a dandy roll. Also
(false) watermarks are made this way.
Jonge Eland papierrestauratie
eland@knoware.nl
t +31 20 623 79 89
f +31 20 627 32 23
VeRes (Dutch Association of Professional Restorers)
postbus 11503
1001 GM Amsterdam
PAPER IS ART IS PAPER IS ART IS PAPER IS ART IS PAPER IS ART IS PAPER