By Carl A Mills © 2008
How could a Stradivarius instrument survive a ship
wreck while a Del Gesù might not? Paolo Perterlongo stated in his book that the
inside of the Strad instruments were treated with waterglass on the inside and
parchment gelatin on the outside, thus water-proofing the instrument. This led
to ossification of the plates to near crystallization, increasing the ability of
the plate to vibrate.
Experiments that I have conducted with three
instruments have not given this same result, but perhaps the passage of time is
also a factor. I did not finish the inside of the instruments I’ve made, and
that could also be a contributing point.
The first step in finishing your instrument is
choosing the type of varnish oil based or spirit based, both have good and bad
properties. It does have to be a good quality varnish. Applied correctly and
with care, it will give the instrument its final appearance and protect it from
damage. The effect on the tone is proportional to the thickness and hardness of
the varnish.
If the finish is poor, the instrument will be refused
by most players and collectors, even if the sound is excellent. Applying a good
transparent varnish is not an easy task. The Builder/Artist in us will determine
the final look of the instrument. Remember, your name is going to be it for many
years, so the instrument will be used to judge your skill and artistic ability.
My best advice to you is to research the finishing
process of wood products as much as possible. Make your decisions based on the
facts, but most of all protect your health.
Safety Precautions
You are responsible for your health and safety.
Without them you will end up a train wreck with many expenses that could have
been avoided. Read and understand all safety precautions related to the tools
and chemicals you use. Obtain MSDS (Material Safety Data Sheet) on all glues and
chemical compounds.
Preparation of the instrument
Remove the fittings, fingerboard, string nut, saddle
nut, and pegs from the instrument. Protect the fingerboard mounting surface of
the neck with tape or card stock. This will help prevent damage and varnish
build up on the fingerboard gluing surface.
Inspect the instrument’s surface areas and remove
all excess glue. Check the smoothness of the instrument. Scrape rough areas
smooth. Check for dents and dings in the wood. If there are dents in the
surface, they can be removed or filled.
To remove a dent in the wood you need a small iron
that will heat up to 175 degrees F. After the iron is hot, place a small drop of
water on the dent and let it soak into the wood. Then apply the iron to the dent
with a piece of cotton cloth to protect the wood. Wait 30 seconds and remove the
iron. Inspect the dent. The steam created by the iron heating the moisture in
the wood will cause it to expand, pushing the dent up. Use a scraper to even out
the surface.
Scraping
Why use scrapers? Scraping will remove wood from both
ring and pulp wood at the same rate, whereas sanding with abrasive paper will
lower the pulp wood faster then the ring wood. This is apparent when the varnish
is applied and valleys appear in between the ring wood.
Figure 27
Figure 27 is a representation of the sanded and
scraped surface of wood viewed from the end grain. The scraped surface is much
easier to apply the sealer to.
Sealing
Clean the instrument. Remove all dust and wood chips.
Set up your holding fixture in the vise. This supports the instrument during the
drying time. The tapered dowel fits into the end pin hole on the instrument.
Clean your shop to remove all airborne dust.
ENSURE that you set up good ventilation
to protect your health.
Use pore filler
potassium
silicate [waterglass]) to seal the wood. As the arching is carved, the end grain
is exposed in the upper and lower bouts. The pore filler comes premixed in a 2
oz. bottle. One bottle will seal two to three coatings depending on the
application method. The pore filler will also accent the grain pattern of the
wood.
Use cloth pads to apply the sealer. Wipe from the end
block to the neck in the grain direction. Use one cloth pad per wipe; this will
give a clean even flow of the sealer onto the instrument. Do not seal under the
neck. Neck stain will be used later to do this. Allow to dry for 24 hours before
a second coat is applied. When dry, use a synthetic abrasive pad to give the
surface a satin finish. The second coat is applied using the same procedure.
After the drying time has passed, inspect the instrument for thin or missed
areas of sealant. Apply a third coat if necessary. Flatten the seal coating
using the micro-mesh system wet sanding method (Follow the instructions supplied
with the kit). Ensure that no water enters the instrument through the
sound-holes.
Varnish Application
The varnish is applied to the instrument by spraying.
The drying time is 48 hours in between each coat. This allows the varnish to
harden enough not to gum up the micro mesh abrasive pads. Apply six color coats
and six clear coats, depending on the depth of color you’re looking for. With
build-up of more than 0.05 thickness of the finish, tone output will be lowered
due to lack of flexibility.
After the first coat, use the abrasive synthetic pad
for a satin finish. This allows the next coat to adhere to the surface. Second
coat is micro-meshed with 800 grit, then use 1000, 1200, 1400, 1600, 1800 and
2000 grit wet sanding with each successive coating, ensuring that no water
enters the instrument through the sound-holes. Allow 48 hours drying time
between each coat. Polish with 5000-10000 grit micro-mesh and wipe the
instrument clean. Use neck stain to finish under the neck. Neck stain is still
elastic after drying, so this allows the neck to flex without damaging or
causing cracks to appear in the varnish.
Let the instrument hang in the daylight out of direct
sunlight. The final color will come out in about three days, because some of the
color may fade. After 48 hours of drying time, polish the instrument with pumice
and rottenstone to the desired finish. Reinstall the fittings as previously
directed in chapter 10. Use a thin viscosity, even coat of hide glue to attach
the fingerboard, string nut and saddle nut.
Polishing and Rubbing
This is perhaps the most tedious and tricky process of
the making of a stringed instrument. It can be used to apply a complete finish
to the instrument and to repair cracks and damage. The method is simple in its
explanation and difficult in its execution. Use of wax based oil is not
recommended on instruments. Linseed oil will darken with age. I recommend you
use a ½-pound cut shellac as the type of varnish.
Directions
Use a three inch square section of lint free cloth
folded into quarters or a felt pad. Set up the ingredients for easy access. Wear
a respirator to protect your health from the dust and solvents used.
Add a small amount of baby oil to the cloth wetting it
thoroughly. Squeeze out the excess oil. The oil acts as a lubricant for the
varnish. Place into a lint free polishing cloth.
Dip the polishing cloth into the varnish mixed with
the solvent 50/50, picking up a small amount of the varnish.
Dip the tip of the varnish cloth into the rottenstone
(as desired), picking up the least amount required for the section you’re
working on.
Start at the neck under the finger board location,
moving in small circles as you work toward the bridge.
As the varnish is applied, the cloth will start to
stick. Remove the cloth and reload it.
Continue the process until the entire instrument is
completed. Allow to dry for 7-14 days in a well ventilated, warm,
humidity-controlled environment. This allows the varnish to harden sufficiently
to withstand the pressure from the bridge feet without leaving an indentation in
the varnish.
To complete, rub out the finish with a lint-free
cloth. The instrument should have a smooth finish and not be too shiny.
Last update
