Demystifying Shellac
I agree, but all in all, it's not a bad shellac write up (as noted it was
taken from the Rosewood Studio website) to pass along to shellac newbie's.
Cheers
Andy
"Bay Area Dave" wrote in message
om...
I was with you right up to the "tack rag"...there's more con than pro
for using a tack rag, A.D.
dave
A Dubya wrote:
Here is a little info on shellac that may be helpful and or informative.
Prior to any finish the wood must be adequately prepared for finishing.
This
means that we hand plane the surface until it is completely smooth. You
can
go directly to finish if you like the effect of leaving some fine tool
marks
on the surfaces of your work. If you want to have a perfectly flat,
smooth
surface, sand the planed surface with 400-grit sandpaper. Remove the
dust
with your bench brush, and then with a tack rag. You may wish to vacuum
off
the wood, but remember to hold the vacuum nozzle off of the surface.
Wipe
the surface with a clean cotton rag.
Shellac is a classic finish that can be applied with a minimum of
difficulty. We choose to mix our own shellac so that we can control the
"cut" or the amount of shellac in solvent. A good solvent to dissolve
shellac flakes is denatured alcohol (ethanol with methanol added). This
is
readily available a hardware stores in USA, but not so in Canada. The
use of
ethanol is a safe process, since this is the same non-toxic alcohol used
in
liquor. Some manufacturers use isobutanol to retard the drying time of
the
finish, which improves workability as the shellac mix is applied to the
wood. Behkol is a commercial product from the Behlen Company, which
contains
95 % anhydrous ethanol, and 5 % isobutanol. Other products used to
dissolve
shellac that are available in Canada are the Lee Valley Shellac solvent,
or
methyl hydrate.
Shellac is actually a secretion of the "lac bug" know technically as
"Laccifer lacca". These insects live in trees in India and Thailand.
They
feed off the sap in the twigs, and then secret a cocoon - type shell
which
is the source of our shellac. Workers shake the tree branches to
dislodge
the cocoon, thus harvesting raw shellac know as sticklac. In this form
it is
unrefined, and will include pieces of twigs. The shellac is then refined
to
remove the debris, and to reduce the natural wax in the lac. Excess wax
reduces clarity in the finish, and reduces moisture resistance in the
finish.
There are several grades of shellac. Orange shellac is a mid grade with
about 4 % wax content. This grade can be used on dark woods, where the
orange color does not change the color of the wood. Orange shellac is
less
refined, and is therefore less expensive than blonde shellac. Blond and
Super Blond shellac is highly refined, such that the wax content is down
to
1%. The flakes are light yellowish brown in color. The dewaxing and
bleaching is achieved by bubbling Chlorine gas through the shellac. This
is
the desired shellac for most fine furniture applications.
Mix your blonde shellac in a small jar with ethanol. It will take
several
hours to dissolve the flakes. Determining your desired cut is an
empirical
process. You simply look at the color of the mixture using window light.
We
typically use two cuts - one for thin wash coats that is thinner, and a
thicker cut for quickly building coats of shellac. The color may be
described as looking like "thin apple juice". If you have excess shellac
in
your mix, you will notice that your pad begins to stick to the wood as
you
attempt the padding process. If this occurs, simply add more solvent.
Note
that shellacs have a shelf life of about 6 months, so mix the shellac
when
you need it. Old shellac develops gummy substances during a process
called
esterification where organic acids react with the alcohol. The net
result is
that the mixture will not cure properly.
Application of the shellac is done as a simple padding process. Make a
"pillow" out of a clean white cotton rag that is about 12 inches square.
Continuously fold in the corners to make a rounded pillow. Apply your
shellac mix to the bottom of the pillow, and then gently wipe the pad
across
the wood, with the direction of the grain. Use a technique of landing
like a
plane - touch the wood going right to left at about 1/3 of the distance
from
the right side of the board. Run the pad across and off the left side of
the
board. On the next pass, start the padding coming from the left side,
landing on the wood 1/3 of the distance from the left side of the board,
and
running right off the right side of the board. Work from the far side of
the
panel towards yourself, indexing by ½ of the pillow width per pass. The
pillow should be moist, but not wet. Recharge the pillow periodically to
ensure that you continue to lay down shellac, and that the surface of
the
pad in moist, but not dripping wet. Excess shellac mix in the pad will
cause
the previously applied shellac layers to be re-dissolved, which defeats
your
building process.
After the first coat, allow the panel to dry for 15 minutes. Shellac
dries
quickly due to the high alcohol content. If the wood feels cool, the
shellac
is not dry enough to proceed. Apply a second thin coat and allow this to
dry
15 minutes to ½ hour. We will eventually build up 7 or more coats, and
the
drying time will increase as the coats build. Apply a third coat and
allow 1
hour for it to fully dry. Cut back the finish now with 0000 steel wool.
Cut
about a foot of steel wool off of your roll, and fold it twice to make a
hand sized pad for burnishing your finish. This process will knock down
any
raised grain, and flatten the surface. Use Liberon brand cabinetmakers
steel
wool without petroleum based oil in it - these oils adversely affect
your
finish. Apply a 4th coat, and allow it to dry 2 hours. Burnish the
surface
lightly with 0000 steel wool. Wipe off the steel wool debris with your
bench
brush, and then dust off the surface with a clean cotton rag before the
next
layer of shellac. Add the 5th, 6th, and 7th layers with 6 hours of
drying
time or more between them. Burnish the surface with steel wool between
each
layer, and then again after the 7th and final layer. You will now have a
satin sheen that is extremely smooth. If during the steel wool process
you
feel a gummy surface, you will have to extend your drying time between
layers to allow the shellac to fully cure.
A fine wax is sometimes applied on top of shellac. One such wax is
Clapham's
bees wax. This is a natural bees wax mixed with Carnauba wax to improve
luster. Apply a thin coat of wax in a circular motion with a clean
cotton
rag in the shape of a pillow. Brush out the wax by making linear strokes
with the grain - in the same fashion as the padding process for shellac.
Burnish the surface with steel wool immediately after applying the wax -
this puts a scratch pattern into the wax to achieve a satin finish.
Brush
off the steel wool debris with your bench brush, and then with a clean
cotton rag. Buff the wax with a clean cotton rag. You will have achieved
a
wonderfully smooth satin finish.
Maintenance
If the surface has minor damage, you may steel wool the surface, wax the
surface, burnish with steel wool, and then buff the surface with a clean
cotton rag.
Taken from Rosewood Studio
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