This information is reprinted from the Cranberry Corner column of Hand Papermaking Newsletter #51 (July, 2000).

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Preparing Pulp

This time we will discuss preparing the pulp and start to describe how handmade paper is made.

MAKING PAPER BY HAND. Up until the paper machine was invented by Nicolas Louis Robert and patented in 1799, all paper had been made by hand.1 Today there exist very few commercial mills in Europe and the Americas where paper is still made by hand, and these are usually associated either with museums, or with small family businesses making high quality specialty papers. In Asia and the Far East there are more small family businesses but these too are declining rapidly in numbers.

HANDMADE PAPERMAKING METHODS. There are two major handmade papermaking methods. These are called Western or European, and Oriental or Japanese. At Cranberry Mills only the Western method is used and this method will be described here.

PULPING. In a non-integrated handmade papermill, dry sheets of pulp are bought from a pulp mill in as large as 200+ kg bales. This is mixed with water and broken up into a fibre suspension with extreme agitation at a consistency (% solids) of one to two percent in either a hydropulper or directly in a Hollander beater.

PULP ADDITIVES. After the pulp to be used for papermaking has been beaten to the desired degree of hydration, as measured by a Canadian Standard Freeness, a Schopper-Riegler Tester, or a Drainage Tester,2 several additives may be mixed with it while under agitation in the pulper or beater.

For archival papers, in order to counteract the effect of ambient acid gases such as sulphur dioxide (SO2) which may be present in the air in which the paper is stored or used, a buffer such as magnesium carbonate (MgCO3) or calcium carbonate (CaCO3) in powder form is added to the pulp.

For calligraphy, stationery, printing, printmaking, woodblock printing, and watercolour art paper grades, a neutral internal size is also added. For facial tissues, towels, wipes, tea bags, and filter papers, etc., a wet strength additive will also be required.

If the paper is to be coloured, a pH neutral pigment must be used. In order to bond it to cellulose fibres, a neutral retention aid must first be added. For added whiteness and higher paper opacity, fillers such as titanium dioxide, kaolin, or talc may also be added.
For non-archival coloured papers, substantive organic dyes, or dyes requiring a mordant to bind them to the fibres may be used.

SCREENING THE PULP FURNISH. Before transferring the pulp to the vat it may by screened to remove foreign materials. This is usually accomplished, in large commercial handmade papermills, by passing the diluted pulp through a stainless steel, slotted, flat screen. Passage of the fibres through the screen is facilitated by a vibrating diaphragm located under the screen.

The disadvantages of this equipment are that it is an expensive machine and that the pulp must by rethickened prior to its entering the vat. A screen would also remove any artistic inclusions such as flower petals and grasses, etc., and so would have to be bypassed while making such grades of paper.

THE VAT. After preparation, the pulp is transferred from the pulping vessel or beater to the vat and its consistency (percent solids) is adjusted to 0.5% to 1.0% depending upon the paper basis weight (pounds per ream), or grammage (grams per square metre) required.

The vat is a tub which is made large enough to easily accommodate the size of the papermaking mould being used. At Cranberry Mills we have four different sized vats which provide for considerable process flexibility. The vat is set up at a height that is comfortable for the papermaker when he or she bends over it to introduce the mould.

The beaten pulp is heavier than water and it will quickly settle to the bottom of the vat. To prevent this, in large commercial handmade paper mills, the vat has a mechanically driven rotating stirring mechanism called “The Hog”3 which extends across the bottom of the vat to keep the pulp from settling. In small mills like ours, a paddle is used to stir the pulp in the vat just before introducing the mould.

References: 1Paper in the Making, G. Caruthers, The Garden City Press, Toronto, 1947. 2Pulp & Paper Manufacture, Preparation & Treatment of Pulp, Canadian Pulp & Paper Association, Montreal, Canada, 1983. 3Making Paper, B. Rudin, Rudins, Vallingby, Sweden, 1990.