ZENTRUM FUR BUCH-ERHALTUNG
ZFB ZENTRUM FUR BUCH-ERHALTUNG GmbH MommsenstraRe 7 D-04329 Leipzig Tel.:
(0341)25989-0 Fax:
(0341)25989-99 eMail:
lnfo@ZFB.com internet: http://www.zfb.ccm
Technical Description
Mass Deacidification Process
April 2000
1.
Introduction
With the beginning of industrial paper production more than 150 years ago and the acidic sizing
connected with it, acids were brought into paper. These acids cause the catalytic degradation of
cellulose. Since cellulose is responsible for the mechanical stability of paper, it becomes brittle with
the progress of the cellulose degradation. This process is auto-catalytic, i. e. the degradation process
furthers the formation of new acids and thus, the reaction accelerates itself. The degradation process
can be stopped effectively by neutralisation and the insertion of an alkaline buffer, but it cannot be
reversed. In the later stages of the degradation process other restoration methods become necessary
(e. g. paper splitting) in order to make the paper usable again. This means: the earlier acid
degradation is stopped, the easier and cheaper the treatment becomes.
2.
The process
The deacidification process of the Deutsche Bibliothek comprises three steps.
The first step is the pre-drying of the books, which remain in a closed treatment chamber during the
entire process. The normal moisture content of 5 - 7% is decreased temporarily to less than 1%. The
drying process takes place under vacuum conditions, accompanied by a mild heating to not more
than 50°C. Due to optimisation of the drying technology, the previously used microwave
technology was replaced by a more favourable method.
The drying is followed by the actual deacidification. The books are impregnated with an alkali
solution. The treatment chamber is flooded completely with the treatment chemical.
The deacidification chemicals are alcoholates of magnesium and titanium dissolved in a volatile
sili-cone oil. Due to the previous drying, the closed books standing in the chamber absorb the
solution like a sponge.
After the treatment solution has been drained, the books are dried again. The solvent absorbed
during impregnation dries away, whereas the actual deacidifying chemicals (magnesium and
titanium compounds) remain in the paper.
The entire process takes two to three days. After the books have been removed from the chamber,
they regain lost humidity and return to their normal moisture content. This process is finished after
approx. 3 weeks. During this period the books exude alcohol due to the reaction of the treatment
chemicals with water. Therefore, the treated books are stored in a ventilated room for approx. 3
weeks before being returned to the customer.
3.
Results of the treatment
The acids contained in the paper are neutralised completely by the magnesium compounds. The pH
value of the paper after treatment is raised to 7 to 9. Immediately after the treatment, the pH-value
of some papers can exceed 9 for a short period. This is a passing phenomenon without any negative
affects on the ageing behaviour of the treated paper, in the following moths, the pH of the paper decreases to levels below 9 due to the transformation of magnesium alcoholates and magnesium hydroxides in magnesium carbonate.
After neutralisation of the acids, 0.5 - 2% superfluous magnesium carbonate remain in the paper,
which serves as the alkaline buffer. Thus, acids formed later or introduced into the paper by
environmental influences can be neutralised within the paper. This alkaline reservoir is of great
importance for the ageing-resistance of the paper. Long-term investigations have shown that paper
samples treated according to our process have a considerably longer life when subjected to artificial
ageing than untreated samples.
The different pH values and alkaline reservoirs after treatment can be attributed to the different
individual amounts of acid contained in the paper before treatment. Furthermore, the amount of the
alkaline reserve can be influenced by the concentration of the treatment chemical.
Although in several instances a slight increase in folding strength has been observed in the treated
papers, these results are insufficient to improve the usability of already damaged materials. A restabilisation of these papers is not yet possible by means of mass deacidification technologies. The
most important aspect of the usability of slightly damaged materials is, however, the stability of the
paper against further ageing processes.
ZFB is currently researching the possibility to deacidify and effectively stabilise the papers in one
technological process.
4. Selection criteria for the materials to be treated 4.1 Condition of the materials
In order to make sure that a deacidification treatment makes sense, the paper to be treated should
retain a sufficient stability. If the paper is already brittle, a deacidification treatment is not harmful
but
has only limited benefits for the paper.
On the other hand, alkaline papers are produced since the 1980s which do not require
deacidification.
Therefore, we test the condition of the material upon request. If no treatment is necessary, we report
this to the customer and recommend an alternative treatment, if necessary.
Due to the evaporation of alcohol described above, the books might give off an alcoholic smell even
after the reconditioning period. Chemical analysis has shown that the concentrations are well below
the legal limit and are, therefore, not dangerous from a hygienic point of view. This slight alcoholic
smell will disappear within the following weeks.
4.2. Special materials
As the nature of the treated objects, their cover materials, inks, dyes and papers varies widely, our
prpcess applies treatment parameters which are valid for the majority of materials and ensure
satisfying results. When special books or archival materials have to be treated, a pre-selection is
necessary for safety reasons.
At the same time we are working on the optimisation of the process in order to ensure high quality
results achieved by state-of-the-art machinery and, thus limit the necessity for pre-selection.
Inks and Dyes
The solvent used by our company does not affect inks and dyes in the majority of cases. Thus, the
process is suited ideally for the treatment of archival materials. Only very rarely has a slight
penetration and bleeding of inks been observed. This was the case with blue/purple copy inks dating
from the first half of the nineteenth century.
In principle, it is possible to test in advance whether an ink or dye is suitable for mass
deacidification. The standard procedure includes these tests for the bulk of materials, but not for the
individual document. An individual proposal can be elaborated for individual objects.
Further optimisation of the process is intended to eliminate these problems entirely in the future.
The influence of the deacidification chemicals on iron-gall ink is investigated separately at present.
Leather
The deacidification of leather-bound books is possible in principle. It has to be mentioned, however,
that the leather is degreased during the deacidification, and the leather feels somewhat stiff after
treatment. Therefore, leather bindings are routinely re-greased after treatment. Certain leather
bindings or strongly damaged bindings have to be sorted out previously.
Parchment
Parchment-bound books and documents written on parchment cannot be treated by our process.
Photographs
In principle, deacidification does not alter photographs from a visual point of view. From a
chemical point of view, however, deacidification is unsuited for photographs.
Coated paper
This sort of material does not pose a problem for our process. The treatment of coated papers is
rarely necessary as the coatings are often alkaline. Occasionally, we find coated paper in books so
that these are treated with the book during the process.
Thermal copies
Thermal copies cannot be deacidified, and therefore have to be sorted out before treatment.
Since in this case, not only the paper but also the writing is in danger, the document should be
copied
on an age-resistant media. Please feel free to ask our experts for advise in this matter.
5.
Transport of the books
Upon request by the customer, ZFB organises the transport of the books/archival materials and
takes the books out of the shelves according to the customer's directions. After treatment, the books
are returned to the shelves in the correct order they were taken out.
Of course, the work in the stocks can be carried out by the library/archive itself. In this case, ZFB
provides the orderer with our special book carriages or baskets and only carries out the
transportation. If the orderer wishes to prepare the materials himself, we would ask him to use the
provided containers which can be rented.
A list containing the call numbers should be provided by the orderer. Please feel free to ask for help
in this matter. If no call number list is provided, the documents are delivered according to number
of books/files. Please understand that in this case ZFB cannot take responsibility for the loss of an
individual item, but only for the bulk, i .e. the number of books handed over to us.
On principle, we can guarantee that the books are returned in the order we received them in. Prerequisite for this is that the books are in the correct order in the shelves and are marked by a call
number on the cover. If the call numbers are interrupted, a call number list is necessary which
determines the order of the books. If these criteria cannot be met by the customer, the details have
to be clarified individually.
6.
Quality standard of the mass deacidification system of the German Library
6.1 Guaranteed quality parameters
The described mass deacidification process guarantees the following quality parameters on the
treated objects:
long-term pH-increase to 7 - 9. (Immediately after the treatment, the pH value can exceed 9 for a
short period of time, which does not affect the ageing behaviour of the treated papers.) introduction
of an alkaline reservoir of at least 0.5 Ma-% MgC03 (If alkaline reserves of more than 0.5 MA-%
magnesium carbonate are required, this has to be agreed upon specifically), even deacidification of
the object (Immediately after the treatment inhomogenities of 1 pH-unit cannot be ruled out
completely. These are levelled out very quickly by migration processes.)
6.2 Appearance of the objects
In principle, the exterior appearance of the deacidified collections remains unaltered after a
deacidification. Since certain materials are not suitable for this process, as described in paragraph 4
a preselection is the prerequisite for ZFB to be liable for any damage occurred during the treatment.
Otherwise ZFB cannot be held responsible for any damage caused by the treatment. Should special
risks become apparent during preselection, the orderer is informed by ZFB.
Should in exceptional cases occur slight, often passing alterations of the originals, as a rule, these
can be eliminated by a subsequent follow-up treatment. The following problems may occur: slight
distortions of the cover disappear in the weeks following the treatment, minor white mineral
sediments on certain types of cover materials. Formation of spots on sensitive linen covers and on
the end papers. Exceptionally the foil can come off in laminated covers and form bubbles. Slight
alcoholic smell which completely disappears in the following weeks
As a rule, objects with problematic inks and dyes become apparent before the treatment and are
consequently sorted out. In exceptional cases, a slight bleeding of inks and dyes of individual signatures, notes or stamps may occur. In most of the cases, these bleedings can be removed by
washing.
Slight stiffening of leather covers which can be eliminated by regreasing. Leather bindings are
therefore greased shortly before the treatment. Certain problematic objects with leather bindings are
sorted out before deacidification.
The treatment chemicals can form films on the surface of coated papers, which can become particularly visible in darker areas.
Since the deacidification chemical brings new solid particles into the paper in every deacidification
treatment, some papers may feel somewhat stiff after the process.
6.3 Paper stability
Although an increase in folding strength has occasionally been observed in treated papers, the
results are not sufficient for an improvement of the usability of damaged materials. So far, mass
deacidification does not offer sufficient re-stabilisation of papers of this kind. During the selection
of materials for treatment, it should be made sure that these have a sufficient remaining stability.
Otherwise, the papers should be restored by means of a stabilisation technique such as paper splitting. Please feel free to ask for advise concerning stabilisation methods.
The decisive criterion for the further usability of deacidified materials is an increase of their
resistance against future ageing processes. ZFB is researching the possibility of deacidifying and
stabilising materials in one technological step.
7. Protocol of the treatment and marking of the objects
A protocol is made for every deacidification order stating the date of deacidification and the applied
chemicals. An analysis protocol for a parallely treated test paper is provided as quality standard.
Upon request by the orderer, the treated materials can be marked with a stamp showing the date of
deacidification.
Furthermore, the deacidified books can be marked externally and listed in an electronic data base.
Books that were not deacidified will be marked in the call number list. If no call number list is
provided, a piece of paper is inserted with the note "not deacidified" which remains in the book
until delivery to the customer. The reason for the cancelled treatment is stated in the call number list
or the insert paper (no treatment necessary, treatment cancelled due to material problems or
alternative treatment recommended).
Sample treatment protocoll
Order number:
Customer:
210.1035.00
State Library
Smith road 1
Smithville, 12345
Treatment:
Treatment charge:
Date of deacidification:
Treatment chemical:
Deacidification
17; 18; 19
June 19, June 21, June 23
magnesium and titanium alcoholates in hexamethyl disiloxane
Results of investigation in test paper:
Leipzig, July 4, 1999
ZFB ZENTRUM FUR BUCHERHALTUNG GmbH
* Materials that were not treated or treated alternatively are listed in the call number list or marked
by slips of insert paper.
** In order to demonstrate the acid or alkali contents in the paper all values were transformed in an
apparent MgC03 deficit or surplus.
ZFB ZENTRUM FUR BUCHERHALTUNG GmbH
Amtsgericht Leipzig HRB 13657
Geschaftsfuhrer: Ernst Becker
Ust-ID-Nr.: DE 184448735
Sachsen LB
(BLZ 860 500 00)
Konto 4190
SWIFT SXLB DE8L
Landesbank Baden-Wurttemberg
(BLZ 600 501 01)
Konto 820 75 20
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