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Subject: New spray deacidification solution

New spray deacidification solution

From: Paul Robert Green <lib6prg>
Date: Wednesday, March 17, 1999
CFC solvents provided an ideal carrying medium for organo-magnesium
compounds used in the spray deacidification of archival books and
manuscripts, since they  have a very low reactivity, are fairly
volatile and  have relatively low toxicities. In addition, they have
a low polarities, which means that they absorb very little water
from the atmosphere--crucial to the stability of the spray solution
based on them and aiding the dimensional stability of the treated

Once CFC solvents were banned from widescale commercial use,
however, the search was on for a solvent mixture with the required
properties of the CFC's to replace them at an affordable price. One
commercial alternative was trialed over an extensive period and
proved unsatisfactory, due to its inadequate shelf life; it either
'gelled' in the cylinder, or it slowly decomposed, leaving a residue
of magnesium hydroxide in the cylinder, which blocked both the
pipework and the spray gun. Large amounts of white powdery deposits
of magnesium hydroxide were also often left on treated materials  It
was also unsatisfactory in that it dried too slowly and could, in
certain circumstances, cause inks to run.

As a textile chemist by training, with a PhD in cellulose chemistry,
I was intrigued by this problem and felt sure that a solution could
be found.  At the recommendation of our binders, I therefore
approached Howard Weaver, a paper technologist, to look at the
problem with us. Howard found the problem much more difficult than
he originally thought and many different formulations were trialed
over the following two years.  It seemed almost impossible to
produce a stable single phase solution, which had all the desired
properties--solutions either dried too slowly, caused inks to run or
were unstable in some way.  However, a stop-gap compromise was
reached in that a fairly stable solution was produced, which did
work successfully, but this had to made up in small quantities by
mixing two solutions--one of the major solvents and one of the
organo-magnesium compound. Once mixed, the solution had to be used
up in about 5 days, so this system was not ideal, but it did at last
provide us with the capability of effective spray deacidification

Just as Howard was about to give up on producing a stable
single-phase solution, he had a 'happy accident' and hit upon the
right combination of  environmentally acceptable, safe, low polarity
solvents to solubilise the organo-magnesium compound.  At long last,
we now have a successful alternative spray deacidification solution,
which is supplied in sealed cylinders, ready for pressurising and
spraying. The solution is stable at room temperature, does not leave
residues in the cylinder and has a nominal magnesium content of  4
grams per litre.

We have tested out the new solution (Renaissance HA liquid) on a
wide range of book and manuscript materials over the past 4 months
and so far have had very little problems with it.  It performs
extremely well in deacidifying and alkalising most papers, even as
low as P.H. 3.5, with a heavy spray, leaving an alkaline buffer of
magnesium hydroxide/ carbonate of at least P.H. 8.00  We have had
very little trouble with movement/ bleeding of inks under normal
spray conditions, though we do undertake 'spot tests' if there is
any uncertainty.

We have had no significant problems at all in spraying manuscript
materials, since these dry very quickly.  However, the new
formulation does not dry as quickly as its CFC forerunner, and it
therefore does take sprayed books longer to dry in the fume
cupboard;  we usually leave t hem to dry overnight.  One advantage
of this slower drying time is that the solution can be clearly seen
to 'soak' through the paper rather than evaporating at the surface.
It can thus be claimed that the spray is much more effective in
deacidifying right through the paper, rather than just at the
surface. There can, however, be a build up of magnesium hydroxide on
the edge of the text block or on the covers, but this usually
brushes off once dry with a soft brush.  We have found that spraying
the covers and then protecting them from further spray with melinex
(polyester) sheets helps to reduce this deposit, whilst continuing
to spray the text block, particularly for very thick books.  We
ensure that the tightly bound spine is properly treated by a heavy
spray in the gutter every 50 pages or so, which soaks right through,
and also by spraying down the spine of hollow-back books.  We now
have a very effective way for rapidly deacidifying and alkalising
whole books, without the costly need to disbind first.  We estimate
that over a whole range of books it takes on average 15-20 minutes
to spray a book, at an average cost of stlg10-00 per book
(EURO14-90, US$16-40 excluding staff time), though we have not as
yet worked out the 'cost per page'.

When spraying books, we have occasionally observed a slight
distortion of the paper as the book dries, particularly with very
acidic paper which requires a heavy spray.  However, this distortion
is slight and it is reversible when the book dries, allowing the
book to condition for a day or two in normal storage conditions and
weighting in a pile or in a press overnight takes the distortion
out. In a way, this slight distortion is a good sign, since it also
indicates that the solution is penetrating right through the paper
and is not merely evaporating at the surface. Deacidification and
alkali residues should therefore be occurring at the fibrillar and
molecular level within the cellulose of the paper.

The only other problem we have encountered with this solution is
with older coated papers, particularly plates in Victorian cookery
books. We think that these are coated with egg albumin.  These
coated papers do have a slight tendency to 'stick' when drying, but
the problem can be overcome by interleaving sprayed plates with
melinex sheeting. Modern coated papers do not seem to be a problem.

We are extremely pleased with this new spray formulation; for
further technical details and availability, contact:

    Howard Weaver,
    Renaissance Chemicals Ltd.,
    Holly House,
    Brayton Lane,
    Selby, North Yorks YO8 9DZ
    +44 1757 703852
    Fax: +44 1757 212101

    **** Moderator's comments: On my request, Paul provided the
    following additional info:

        HA is a proprietary solution manufactured by Renaissance
        chemicals and even I don't know the exact formulation. We
        don't have any commercial interest in Renaissance Chemicals
        ourselves, but I have been working closely with Howard
        Weaver over the past few years to try and solve the problem
        of stable organic deacidification solutions which are CFC
        free.  Although I know roughly what's in 'HA solution', the
        exact formulation is his 'trade secret' -- He obviously
        wants to market it commercially and to keep ahead of the
        field, the formulation is not available

        HA liquid is available in the UK, but is still to be
        packaged and licensed for sale abroad--I think it likely
        that Howard will look for a distributor, possibly to sell
        the product in smaller quantities as an aerosol, but he's
        still at an early stage.

Dr. Paul R. Green
Conservation Officer
Leeds University
Leeds LS2 9JT UK
+44 113 233 6375
Fax: +44 113 233 5561

                  Conservation DistList Instance 12:76
                  Distributed: Friday, March 26, 1999
                       Message Id: cdl-12-76-004
Received on Wednesday, 17 March, 1999

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