Z-factor
technical paper no 3: Ethyl silicate 40 as Binder in Mural Painting.
Text and illustrations: Gijsbert Witkamp*
The original text dates back to around 1977. It
has been edited for this I-net publication.
Present update: 16 December 2016
 |
| Photo 1. Made in the Netherlands. G. Witkamp, 1974, 12 x 8 m, E 40 mural paint |
Introduction
The author in 1974
designed and executed a 12 x 8 m2 outdoor mural in the city of
Leeuwarden, Netherlands, using studio
made paints having ethyl silicate 40 (E40) as binder. This probably was the
first or one of the first uses of this medium in mural art in the Netherlands. A
few years later he tested the same material in Lusaka, Zambia, when he was
requested to submit a mural design for one of Lusaka’s high rise office buildings. E40 paint, though relatively unknown, has a number of superior qualities
compared to other mural paints. It hence is an important addition to the small
range of mural paints suitable for durable art work. The paint is best applied
indoors. Outdoor lasting application should be under a canopy that protects
from rain and wind.
History
Ethyl silicate was
first synthesized in 1846. Suggestion for the application of silicon esters for
the preservation of stone objects and architectural structures was made in 1860
though it was not until 1923 that the first practical work was initiated by A.P.
Laurie and G. King (1930, 1931a, 1931b). They set out practices for the use of
silicon ester in stone conservation and mural painting. Presently a variety of
silicon esters are industrially produced for applications in paints, investment
casting and stone reinforcement.
Paint
making
E40 is used as raw
material that produces a colourless, hard, porous and inert binder for mural
paints. The actual binder is silica (SiO2, sand is the most common
form of this compound). E40 is a silicon ester that yields a high percentage of
silica. The chemical bond between silica and ethyl alcohol is broken by
hydrolysis. The silica turns into a gel which later becomes a hard, permanent
silica film.
The preparation of
E40 paint in the studio is well described by R. Mayer (1982: 346-354) as well
as its properties and application in art work. The paint, in brief, is prepared
as follows. Pour 80 vol. units of E40 in a non-ferrous vessel and mix with 18
vol. units of ethyl alcohol and 2 vol. units of 95% (190 proof) hydrochloric
acid (HCl). Agitate for twenty minutes and let stand for 12 hours. During this time
E40 is partially hydrolysed, HCl acting as catalyst. Now add 5 vol. units
of water. Hydrolysis should thereafter be complete in eight to twelve hours.
This can be checked by applying a thin film on glass. The film should dry
rapidly and craze when scratched.
At this stage pigment and
micronized mica must be added, roughly a quarter by weight of each. The
simplest method is to add pigment and mica to the liquid while stirring with a
stick. For this a plastic bucket with lid is quite suitable – as the paint
should be applied soon after mixing. In industrial practice a ball mill is used
ensuring perfect dispersion of particles in the liquid. Mixing is easy as the medium
has good wettability and this is why the simple manual method yields acceptable
results. The mica acts as filler and improves paint consistency – without it the
paint is quite liquid and harder to handle.
Paint
properties
Once mixed the paint
has to be used within 24 hours as the impending gelling and solidifying stages
cannot be retarded. Gelling obstructs adherence.
The silicon binder
forms a porous, cementitious bond between pigment and support. The pigments
therefore largely retain their natural appearance as there is no coating causing
refraction of light. The resulting mat surface suits mural painting very well.
The porosity allows the wall to breath and contributes to the longevity of the
paint. Destruction of the paint is brought about by mechanical wear (as by rain
drops or air born dust particles), deterioration of the support, improper application
of the paint and possibly its inherent brittleness. As a plasticizer 2-4% polyvinyl
butyral (vinylite XYHL) has been added.
The paint sets
within a few minutes and is dry to the touch within 24 hours. The entire “drying”
process takes one to three months to complete.
Painting
Prior to painting
the proposed wall surface needs to be inspected. There should be no
efflorescence or leakage; the surface should be intact, clean and not covered
by paint or other film making substance. The surface usually is lime or cement
plaster or perhaps concrete. All these are suitable. Normally a ground coat of
white paint is first applied. This shall increase the luminosity of the work. Over
painting can be done after a couple of hours. There is limited opportunity for
wet-in-wet painting due to the drying speed of the paint.
E 40 paint has to
be applied thin and fresh. Thick and multiple layers have poor adherence and eventually
flake off or crack. The paint is thinned with a mixture of one part E4o medium
and three parts ethyl alcohol. Fresh paint can be wiped off with ethyl alcohol.
Brushes must be cleaned immediately after use by rinsing in ethyl alcohol. The
thoroughly dried paint film can be cleaned with water and brush.
Pigments
For permanent art work
standard pigments have to be used that are both alkali and acid resistant.
These are: titanium dioxide (white), the iron oxides or mars colours (yellow,
reddish brown, black), chromium oxide (dull green), viridian (bright green), cobalt
blue, manganese blue and caeruleum blue. Under less stringent conditions
phtalocyanine blue, ultramarine blue and the cadmium colours (yellow-orange-red
range) are also used. Note that the cadmium pigments are poisonous.
Precautions
Prolonged exposure
to E40 is harmful to human health. Work and prepare paint in ventilated areas. Incidental
skin contact is not particular harmful, clean with ethyl alcohol. Ethyl alcohol
is flammable and poses a fire hazard. Presence of a fire extinguisher is advisable.
Need
for experiments
Artists considering
to work with E40 first should try the medium out by making small quantities of
paint and applying these to concrete tiles, bricks or slabs. These should be
exposed to outdoor condition once fully hardened. Test carried out by the
author in Zambia demonstrated the strength of the paint: tiles exposed to
weathering under adverse conditions for several years displayed remarkable durability
though mechanical wear and tear was observed. Also the importance of applying
the paint in thin layers was confirmed; thickly applied paint tends to crack or
flake off.
Comparison
to other mural paints
The main paints used for murals are oil
paints, acrylic paints, pva’s, waterglass, and casein paints. Fresco is an
ancient technique and is water based. Oil paints are not suited for direct
application to walls. Acrylic paint, like oils, forms a continuous paint film
which prevents the wall from “breathing” and thus may cause deterioration of
the paint film. Water glass, E 40, pva and fresco don’t seal the wall surface
and therefore are structurally better. Casein paints are optically not as
pleasing as fresco, E 40 or pva. Pva in commercial grades does not meet
artistic quality standards, b
ut is fine for
temporary work. Waterglass painting, also named Keim’s process after its
inventor, like E 40 has a silica binder; however the process involves the presence
of the highly reactive elements sodium or potassium. Fresco is the standard in
the Western art mural tradition. The technique, however, is very laborious,
requires considerable technical skill and experience, and is more rigid than E
40.
Supplies
E 40 is produced by Dynamit Nobel Aktien
Gesellschaft and Union Carbide Ltd. Standard pigments have to be supplied from
specialised houses, in particular those that only are used in artistic
practice. Ethyl aLcohol and hydrochloric acid are procured from chemical
suppliers. All can be googled up.
* The author is an artist and cultural anthropologist working
in Zambia. He produced several murals of which one in ethyl silicate 40. He is
the founding director of the Choma Museum and Crafts Centre and organized
several art exhibitions in Zambia. He publishes mainly on The Net; mostly in the Art in Zambia Blog, the Z-factor Art Site, Z-texts
on line and www.academia.edu.
References
and bibliography
Cogan, H.D. and C.A.
Setterstrom. Properties of Ethysilicate. In Chemical
and Engineering News, 24 (18), 25 Sept. 1946.
Cogan, H.D. and C.A.
Setterstrom. Ethylsilicates. In: Industrial
and Engineering News. 39 (11), 1947.
King, G. Silicon
Ester Binder. In: Paint Manufacture,
April 1931.
King, G. Silicon Ester Paint Medium. In: Paint Manufacture, May 1931.
Mayer, R. The Artists’ Handbook of Materials and
Techniques. New York: Viking Press. 1982.
