finished panel may be less objectionable with the furrows in parallel
lines than in what engravers call “cross-hatching,” but if the rubbing
is properly done it is not easy to discover what difference it could
make whether the stone is moved in a straight line or a circle. As to
absorption, it cannot be distinguished in the finished panel between
the surface that was coated with liquid filler and that to which the
color was applied directly, except that cracking always occurs much
sooner in the former, and this will be found to be the case with
surfaces that have been coated with liquid filler and finished without
roughstuff. Among the pigments that may be used for roughstuff, and
there are half a dozen or more, any of which may be used with success,
there is no doubt but that known as “English filler” is best, but it is
not always to be had without delay and inconveniences.
Yellow ocher, Reno umber and Keystone filler are all suitable for
roughstuff, the ocher having been used many years for the purpose,
but, as already remarked, the English filler is best. This is the
rule for mixing given by Nobles and Hoare: Four pounds filler, 1
pound ground white lead, 1 pint gold size, 1 pint varnish and 1 1/4
pints turpentine, or 3/4 pint good size and 1/2 pint boiled oil
in lieu of the varnish. In regard to the use of white lead ground in
oil, it makes the rubbing more laborious, increases the liability
to scratching, and requires a much longer time to harden before the
scouring can be done, without in any appreciable manner improving the
quality of the surface when finished.
It may be remarked here that the addition of white lead, whether
ground in oil or added dry to the coarser pigment, increases the labor
of scouring just in proportion as it is used until sufficient may be
used to render the scouring process impossible; hence, it follows that
the mixing should be governed by the character of the job in hand. If
the job is of a cheap class the use of very little or no lead at all
is advisable, and the proportion of Japan and turpentine may also be
increased, with the result that a fairly good surface may be obtained
with much less labor than in the formula given.
The number of coats of filler required to effect the purpose in any
given case must depend upon how well the builder has done his part
of the work. If he has left the surface very uneven it follows, as a
matter of course, that more coats will be required to make it level,
and more of the roughstuff will remain after the leveling process than
if the woodwork had been more perfectly done. While the merits of a
system or method are not to be judged by its antiquity, there should be
a good reason to justify the substitution of a new method for one that
has given perfect satisfaction for generations and been used by the
best coach painters who ever handled a brush.
A well-known writer on paints says that the effect of a varnish is
usually attributed to the manner of its application and the quantity
of thinners used for diluting the melted gums, with the prepared oils
and the oxidizing agents used in its manufacture. While this has
undoubtedly much to do with the successful application of varnish,
there are other facts in this connection that should not be overlooked.
For example, varnish is sometimes acted on by the breaking up, or the
disintegration of the filling coats; which in turn is evidently acted
on by the wood itself, according to its nature. {774}
With the aid of the microscope in examining the component parts of
wood a cellular tissue is observed which varies in form according to
the species and the parts which are inspected. This cellular tissue is
made up of small cavities called pores or cells, which are filled with
a widely diversified matter and are covered with a hard and usually
brittle substance called _lignin_.
This diversified matter consists of mineral salts and various
organic substances, gelatinous in their nature and held in solution
by a viscous liquid and containing nitrogenous matter in different
combinations, the whole being designated by the general name of
albuminous substances. The older the wood the more viscous is the
matter; while wood of recent growth (sapwood) contains less viscous
matter holding these substances in solution. This albumen in wood acts
on substances like filler and varnish in one way or the other, good
or bad. The seasoning of wood does not dispose of these substances.
The water evaporates, leaving them adhering to the sides of the cells.
The drier these substances are the less action they exert on the
filler or whatever substance is coated on the surface. If the filler
disintegrates, it affects the varnish.
All albuminous substances, be they dry or in liquid form, are subject,
more or less, according to the protein they contain—which seems, or
rather is, the essential principle of all albuminous matter—to the
influence of caustic potash and soda. Thus, the albumen of an egg is
exactly like that contained in the composition of wood. As albumen in
wood becomes solid by drying, it is easily dissolved again, and will
then be acted on chemically by any extraneous substance with which it
comes in contact.
Some of the shellacs, substitutes for shellacs, and some of the liquid
fillers are manufactured from some of the following substances: Old
linseed oil, old varnish, old and hard driers, turpentine, benzine,
often gasoline, rosin, whiting, cornstarch flour, nulls, paint
skins, silica, and so on. The list is long. To these must be added a
large volume of potash, to bring it to and hold it in solution. There
must be an excess of potash which is not combined into a chemical
compound, which if it did, might mitigate its influence on the albumen
of the wood. But as there is potash in its pure state remaining in
the solution it necessarily attacks the albumen of the wood, causing
disintegration, which releases it from the wood, causing white, grayish
flakes, and the formation of a powder. This is not a conclusion drawn
from an inference but an established scientific fact resulting from
experiments with fillers the various compositions of which were known.
All alkalies act on albumen. No one would knowingly varnish over a
surface such as it would be were the white of an egg applied to it and
then washed with an alkali solution; but that is just what is done when
varnish is put over a wood surface filled with a filler which contains
an alkali.
Most of the combinations of material used in the painting trade are
mixtures; that is, each part remains the same—exerting the same
chemical action on another substance, or any other substance coming in
contact with a paint mixture will exert the same chemical action on any
part, or on any ingredient it contains, the same as if that part was by
itself.
We can now account for some of the numerous peculiarities of varnish.
We know that any alkali when coming in contact with albumen forms
a compound, which on drying is a white, brittle substance easily
disintegrated. This is why potash, sal soda, and kindred substances
will remove paint. The alkali attacks the albumen in the oil, softening
it, causing easy removal, whereas if it were allowed to dry, the
albumen in the oil would take on a grayish color quite brittle. Potash
or other alkalies in filler not only attack the albumen in the wood,
but also attack the albumen in the oil by forming a compound with it.
Probably this compound is very slight, only forming a compound in
part, enough, nevertheless, to start a destroying influence, which is
demonstrated by the following results of experiments. The reader has,
perhaps, some time in his career applied a rosin varnish over a potash
filler and has been surprised by the good results, a more permanent
effect being obtained than in other instances where the best of varnish
was used. This is accounted for by the rosin of the potash. Again, the
reader may have had occasion to remove varnish with potash and found
that potash would not touch it. This is because of its being a rosin
varnish. Potash in filler may be rendered somewhat inert, by reason
of its compounding with other parts of the filler, but owing to the
quantity used in some of the commercial fillers it is not possible that
all the alkali is rendered inert. Hence it will attack the albumen
wherever found, as all albumen is identical in its chemical composition.
Alkalies have but little effect on the {775} higher classes of gums,
because of their effect on the albumen in the wood and oil. All
alcohol varnishes or varnishes made by the aid of heat stand well over
an alkali filler. Varnishes which contain little oil seem to stand
well. This is accounted for by the fact that alcohol renders albumen
insoluble. Alkalies of all kinds readily attack shellac and several
other of the cheap gums, forming unstable compounds on which oil has
but little effect.
Close-grained wood contains less albumen and more lignin than
open-grained varieties, and consequently does not take so much filler,
which accounts for the finish invariably lasting longer than the same
kind used on an open-grained wood. Open-grained wood contains more sap
than close grained; consequently there is more albumen to adhere to the
sides of the cells. The more albumen, the more readily it is attacked
by the potash, and the more readily decomposed, or rather destroyed.
Alcohol renders albumen insoluble immediately on application. It
prevents it from compounding with any other substance, or any
other substance compounding with it. Hence, we must conclude that
an application of alcohol to wood before the filler is applied is
valuable, which is proven to be a fact by experiment. Wash one half of
a board with alcohol, then apply the potash filler over all. Again,
wash the portion of the board on which is the filler and apply a
heavy-bodied oil varnish. Expose to sunlight and air the same as a
finished door or the like, and wait for the result. At the end of a few
months a vast difference will be found in the two parts of the surface.
The one on which there is no alcohol will show the ravages of time and
the elements much sooner than the one on which it is.
Wood finishers demand a difference in the composition of fillers,
paste and liquid, for open- and close-grained wood, respectively; but
unfortunately they do not demand a difference between either kind
in themselves, according to the kind of wood. Paste fillers are used
indiscriminately for open-grained wood and liquid for close-grained
wood.
To find the fillers best adapted for a certain wood, and to classify
them in this respect will require a large amount of chemical work and
practical experiments; but that it should be done is evidenced by the
fact that both success and failure result from the use of the same
filler on different varieties of wood. After once being classified
(owing to the large number now on the market), they will not number
nearly so many in the aggregate as might be supposed; as it will be
found in many instances that two entirely different varieties of wood
resemble each other more closely in their vascular formation and cell
characteristics than do two other specimens of the same variety. It is
a recognized fact that paste fillers whose base is starch or the like
work better and give better results in certain instances, while those
whose base is mineral matter seem to do better in other cases.
It is noticed that rosewood as a finishing veneer is obsolete.
This is not because of its scarcity, but because it is so hard to
finish without having been seasoned for a long time. In these days,
manufacturers cannot wait. It takes longer for the sap of rosewood
to become inactive, or in trade parlance to “die,” than any other
wood. This is because it takes so long for the albumen in the sap
to coagulate. Rosewood has always been a source of trouble to piano
makers, on account of the action of the sap on the varnish. However,
if this wood, previously to filling, was washed with a weak solution
of phosphoric acid, and then with wood spirit, it might be more easily
finished. The phosphoric acid would coagulate the albumen on the
surface of the wood immediately, while alcohol would reduce it to an
insoluble state. The idea here is to destroy the activity of the sap,
on the same principle as sappy places and knot sap are destroyed by
alcohol-shellac before being painted.
Oak is another wood which gives the painter trouble to finish. This may
be accounted for as follows: Oak contains a sour acid principle called
tannic acid. It is a very active property. Wood during the growing
season contains more albumen; thus in the circulation of the sap a
large quantity of soft matter is deposited on the lignin which lines
the cells, which lignin, if it contains any acid matter, acts on the
material of the filler. Tannic acid has a deleterious effect on some
of the material of which a number of fillers are made. Starch and many
gums are susceptible to its influence, making some of them quite soft.
Oak, like most other timber cut at the season when the least sap is in
circulation, is the more easily finished.
The vascular formation may, and no doubt has, something to do with
wood finishing. Different species of wood differ materially in their
vascular and cellular formation. Wood finishers recognize a difference
in treatment of French burl walnut and the common American {776}
variety. Circassian and Italian walnut, although of the same species,
demand widely different treatment in finishing to get the best results.
The only way to find the best materials to use in certain cases is to
study and experiment with that end in view. If, by aid of a microscope,
a certain piece of wood shows the same cellular formation that another
piece did which was successfully finished by a certain process, it may
be regarded as safe to treat both alike. If observation on this line is
indulged in, it will not take the finisher very long to learn just what
treatment is best for the work in hand. How often it has been noticed
in something of two parts, like a door, that the panels when finished
will pit, run, or sag, while the sides will present a surface in every
way desirable and _vice versa_. This is due to the difference in the
cellular construction of the wood and to the cellulose, and cannot be
otherwise for the parts have been seasoned the same time and treated
exactly alike. The physiology of wood is imperfectly understood,
but enough is known to warrant us in saying with a certainty that
the chemicals in fillers do act upon the principles embodied in its
formation.
* * * * *
Some tried formulas follow:
I.—Make a paste to fill the cracks as follows: Old furniture polish:
Whiting, plaster of Paris, pumice stone, litharge, equal parts, Japan
drier, boiled linseed oil, turpentine, coloring matter, of each a
sufficient quantity.
Rub the solids intimately with a mixture of 1 part of the Japan, 2
parts of the linseed oil, and 3 parts of turpentine, coloring to suit
with vandyke brown or sienna. Lay the filling on with a brush, let it
set for about 20 minutes, and then rub off clean except where it is to
remain. In 2 days it will be hard enough to polish. After the surface
has been thus prepared, the application of a coat of first-class copal
varnish is in order. It is recommended that the varnish be applied in a
moderately warm room, as it is injured by becoming chilled in drying.
To get the best results in varnishing, some skill and experience are
required. The varnish must be kept in an evenly warm temperature, and
put on neither too plentifully nor too gingerly. After a satisfactorily
smooth and regular surface has been obtained, the polishing proper may
be done. This may be accomplished by manual labor and dexterity, or by
the application of a very thin, even coat of a very fine, transparent
varnish.
If the hand-polishing method be preferred, it may be pursued by rubbing
briskly and thoroughly with the following finishing polish:
Alcohol 8 ounces
Shellac 2 drachms
Gum benzoin 2 drachms
Best poppy oil 2 drachms
Dissolve the shellac and gum in the alcohol in a warm place, with
frequent agitation, and, when cold, add the poppy oil. This may be
applied on the end of a cylindrical rubber made by tightly rolling a
piece of flannel, which has been torn, not cut, into strips 4 to 6
inches wide. It should be borne in mind that the surface of the cabinet
work of a piano is generally veneered, and this being so, necessitates
the exercise of much skill and caution in polishing.
II.—Prepare a paste from fine starch flour and a thick solution of
brown shellac, with the spatula upon a grinding stone, and rub the
wooden object with this. After the drying, rub off with sandpaper and
polish lightly with a rag moistened with a thin shellac solution and a
few drops of oil. The ground thus prepared varnish once or twice and a
fine luster will be obtained. This method is well adapted for any wood
with large pores, such as oak.
«Removal of Heat Stains from Polished Wood.»—Fold a sheet of blotting
paper a couple of times (making 4 thicknesses of the paper), cover the
place with it, and put a hot smoothing iron thereon. Have ready at hand
some bits of flannel, also folded and made quite hot. As soon as the
iron has made the surface of the wood quite warm, remove the paper,
etc., and go over the spot with a piece of paraffine, rubbing it hard
enough to leave a coating of the substance. Now with one of the hot
pieces of flannel rub the injured surface. Continue the rubbing, using
freshly warmed cloths until the whiteness leaves the varnish or polish.
The operation may have to be repeated.
«PRESERVATION OF WOOD.»
I.—An excellent way of preserving wood is to cut it between August
and October. The branches are removed, leaving only the leaves at the
top. The trunks, carefully cut or sawn (so that their pores remain
open), are immediately placed upright, with the lower part immersed in
tanks three-quarters filled with water, into which 3 or 4 kilograms of
powdered cupric sulphate per hectoliter have been introduced. The mass
of {777} leaves left at the extremity of each trunk is sufficient to
cause the ascent of the liquid by means of the capillary force and a
reserve of energy in the sap.
II.—Wood which can be well preserved may be obtained by making a
circular incision in the bark of the trees a certain time before
cutting them down. The woodcutters employed in the immense teak forests
of Siam have adopted in an empirical way a similar process, which has
been productive of good results. The tree is bled, making around the
trunk, at the height of 4 feet above ground, a circular incision 8
inches wide and 4 inches deep, at the time when it is in bloom and the
sap rising. Sometimes the tree is left standing for 3 years after this
operation. Frequently, also, a deep incision reaching the heart is made
on two opposite sides, and then it takes sometimes only 6 months to
extract the sap.
It is probable that it is partly in consequence of this method that the
teakwood acquires its exceptional resistance to various destructive
agents.
III.—A good preservation of piles, stakes, and palisades is obtained
by leaving the wood in a bath of cupric sulphate of 4° of the ordinary
acidimeter for a time which may vary from 8 to 15 days, according to
greater or less dryness of the wood and its size. After they are half
dried they are immersed in a bath of lime water; this forms with the
sulphate an insoluble compound, preventing the rain from dissolving the
sulphate which has penetrated the wood. This process is particularly
useful for vine props and the wood of white poplars.
A good way to prevent the decay of stakes would be to plant them upside
down; that is, to bury the upper extremity of the branch in the ground.
In this way, the capillary tubes do not so easily absorb the moisture
which is the cause of decay. It frequently happens that for one or
another reason, the impregnation of woods designed to be planted in
the ground, such as masts, posts, and supports has been neglected. It
would be impracticable, after they are placed, to take up these pieces
in order to coat them with carbolineum or tar, especially if they are
fixed in a wall, masonry, or other structure. Recourse must be had to
other means. Near the point where the piece rises from the ground,
a hole about one centimeter in width is made in a downward slanting
direction, filled with carbolineum, and closed with a wooden plug.
It depends upon the consistency of the wood whether the liquid will
be absorbed in 1 or 2 days. The hole is filled again for a week. The
carbolineum replaces by degrees the water contained in the wood. When
it is well impregnated, the hole is definitely closed with a plug
of wood, which is sawn level with the opening. The wood will thus
be preserved quite as well as if it had been previously coated with
carbolineum.
IV.—Wooden objects remaining in the open air may be effectually
protected against the inclemency of the weather by means of the
following coating: Finely powdered zinc oxide is worked into a paste
with water and serves for whitewashing walls, garden fences, benches,
and other wooden objects. After drying, probably at the end of 2 or
3 hours, the objects must be whitewashed again with a very dilute
solution of zinc chloride in glue or water. Zinc oxide and zinc
chloride form a brilliant, solid compound, which resists the inclemency
of the weather.
As a paint for boards, planks for covering greenhouses, garden-frames,
etc., Inspector Lucas, of Reutlingen (Würtemberg), has recommended the
following coating: Take fresh cement of the best quality, which has
been kept in a cool place, work it up with milk on a stone until it is
of the consistency of oil paint. The wood designed to receive it must
not be smooth, but left rough after sawing. Two or 3 coats are also a
protection from fire. Wood to be thus treated must be very dry.
V.—Wood treated with creosote resists the attacks of marine animals,
such as the teredo. Elm, beech, and fir absorb creosote very readily,
provided the wood is sound and dry. Beechwood absorbs it the best. In
fir the penetration is complete, when the wood is of a species of rapid
growth, and of rather compact grain. Besides, with the aid of pressure
it is always possible to force the creosote into the wood. Pieces of
wood treated with creosote have resisted for 10 or 11 years under
conditions in which oak wood not treated in this way would have been
completely destroyed.
The prepared wood must remain in store at least 6 months before use.
The creosote becomes denser during this time and causes a greater
cohesion in the fibers. In certain woods, as pitch pine, the injection
is impossible, even under pressure, on account of the presence of rosin
in the capillary vessels.
VI.—M. Zironi advises heating the wood {778} _in vacuo_. The sap
is eliminated in this way. Then the receiver is filled with rosin
in solution with a hydrocarbide. The saturation takes place in two
hours, when the liquid is allowed to run off, and a jet of vapor is
introduced, which carries off the solvent, whole the rosin remains in
the pores of the wood, increasing its weight considerably.
VII.—Wood can be well preserved by impregnating it with a solution of
tannate of ferric protoxide. This method is due to Hazfeld.
VIII.—The Hasselmann process (xylolized wood), which consists in
immersing the wood in a saline solution kept boiling under moderate
pressure, the liquid containing copper and iron sulphates (20 per cent
of the first and 80 per cent of the second), as well as aluminum and
kainit, a substance until recently used only as a fertilizer, is now
much employed on the railways in Germany.
IX.—Recently the discovery has been made that wood may be preserved
with dissolved betuline, a vegetable product of the consistency of
paste, called also birchwood rosin. Betuline must first be dissolved.
It is procurable in the crude state at a low price. The wood is
immersed for about 12 hours in the solution, at a temperature of from
57° to 60° F.