Peak of Flight #17: Coloring Balsa wood with RIT dye
Apogee Components' Peak of Flight newsletter, issue 17. Date: undated; published between 2000 and 2005 (from the neighbouring dated issues).
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Dying To Be Colorful
Using Rite-Dye to Brighten up Sheet Balsa Models
By Andrew Tomasch
Because they are quick, easy, and fun, I build a lot of
models from sheet balsa. This includes model aircraft (hand
launched and catapult launched gliders) and space models
(boost gliders and rocket gliders). My one complaint has always been that there is no really good way to add color to
these models.
The standard spacemodeling practice of rubbing magic
marker over the surfaces produces too uneven a result for my
taste, and covering with japanese tissue adds too much work
(and on small models, weight). Things came to a head when I
wanted to enter a profile scale event at an indoor aircraft meet
and only had time to build a sheet balsa profile Stinson form a
Peck Polymers kit.
The rules for "No Cal" scale clearly state that the model
must have a "reasonable imitation of the original color scheme
and markings." Everyone knows that Stinsons are green and
balsa is not, so I clearly had a problem.
I had heard vague rumors over the years that Rit dye can
be used to color models and I decided that I'd play with some
and see what happened. I chose the direct approach: Mix the
dye in hot water, pour it into a disposable foil pan and dunk
the finish sanded parts into the dye. It worked! I was afraid
of warping the wood, but this was not a problem. If you get
balsa soaking wet and then allow it to dry evenly on both sides,
it doesn't warp, in fact, any warps present before wetting will
still be there after the wood dries.
This first attempt added one hour to the construction time
of the model, and produced a beautifully uniform green color.
Since then I have dyed three more models, one each in yellow, orange, and red, all with equal success. I can now do the
entire dye bath procedure in 30-45 minutes and consider it a
normal step in the construction of an all balsa model.
Here are the steps involved in dying sheet balsa models:
1) Completely finish sand the model to the desired
smoothness, as no further shaping or smoothing can be done
after the dye is applied. The wood must be "raw" without
glue or dope on the surface. The dye will not penetrate the
wood where there is glue present, so if you joined pieces of
wood to make the finished part, be sure that all cement is sanded
off the surface or a white spot will result. Water based glues
such as Tite Bond cannot be used to join parts which are to be
dyed unless the dye is applied first. I use old fashioned cellulose model airplane cement (Sigment or Testors) to join parts,
carefully sanding all the glue off the surface of the joint when
dry.
2) Prepare the area. The dye is very easy to work with,
but spills will cause stains on counter tops etc. Cover the
work surface with newspapers or plastic. It helps to have a
sink as close as possible. I use my bathroom counter top. Lay
out an area of paper towels to blot the parts as they come out
of the bath. Mix up a pint of water with a teaspoon or so of
chlorine bleach to remove any stains which do occur. These
are not serious, no worse than a blueberry juice stain on
formica. I wouldn't spill dye on the carpet!
Have plenty of paper towels ready for blotting/wiping and
a trash bag for the soiled paper towels. The idea is to keep the
dye under control at all times. By working carefully you can
literally complete the process without spilling a drop.
Finally, set up a drying area consisting of a flat table top
covered with aluminum foil, large enough to spread out all
the dyed parts while they dry.
3) Mix the Dye. I use a quart jar and microwave the water until it is very hot. For powdered dye, I use 1/2 - 3/4 of a
package, more for lighter colors, less for darker.
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The liquid dyes work well with 1/2 a bottle in a quart of
water. Since you can intensify the color by leaving the parts
in longer, this is not critical, but it's probably better to err in
the direction of more dye to ensure an adequately deep color.
The only critical part of the procedure is to ensure that
the final dye solution has no lumps of un-dissolved dye in it to
cause streaks on the part. Stir well and pour off the solution
slowly to leave the lumps in the mixing jar. I strain the dye
through several thicknesses of nylon stocking as further insurance. The liquid dyes are particularly nice since they are
not as lump prone, and I highly recommend them.
4) Dye the parts. Pour the lump free dye solution into
your dying pan. For small parts, disposable foil baking pans
are perfect. Plastic storage tubs work well for larger parts.
The dye solution will now be nice and lukewarm. Dunk one
part at a time and keep turning it over and agitating it with
your finger tips. Wear disposable rubber gloves (available at
hardware stores, sold for furniture stripping).
Practice on a piece of scrap first to convince yourself it is
going to work. After a few minutes, you will have a nice
depth of color. Remove the part from the tub, and strip off the
excess solution with your fingers. Place it on the paper towels and blot firmly with more paper towels. This will draw out
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the excess water and remove any dye which is not going to
stay on the part.
Set the part on your foil covered drying space and repeat
the process until all parts are done. Once you get the hang of
it, several small parts can be dunked at once. Just be sure to
keep them moving and keep flipping them over so that all
surfaces take the dye evenly.
5) Drying. Here the trick is to let the parts dry evenly on
both sides. At first I weighted the parts down with glass jars
and drinking glasses to keep them flat, and turned them over
every 10 minutes or so until thoroughly dry. This works fine,
but may not be necessary. The parts will curl the first few
times they are flipped because they will have dried more on
the exposed side than on the side against the table.
Don't panic! Once the parts are really dry they will not be
warped. The most recent model I dyed was not weighted at
all, just placed on the foil and flipped over every 10 minutes.
It dried nicely and never showed any warping tendencies while
drying. I picked up a very slight warp in a thin stabilizer,
which came out with a little hot breath and has stayed out
since the part was doped.
I recommend not weighting down thicker surfaces such
as HLG or boost glider wings and weighting down very thin
What does this mean to you?
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©2002 Hall Consulting
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surfaces. Stand the thicker surfaces on edge. Use glass for
your weights, as metal might discolor your pretty finish. Be
careful not to dent the wood.
6) Clean up. CAREFULLY pour the dye down the drain
while running plenty of water from the tap. The dye solution
seems to deteriorate if stored, so don't bother trying to save it
for more than a few days. The dye solution will not stain a
sink if it is clean and the dye is washed away quickly. It also
washes out of the foil pans and plastic tubs easily and leaves
no staining, so your tubs can be re-used. I store my dying
supplies in my large plastic storage/dye tub. Minor stains on
counters can be cleaned up with the bleach solution mentioned
earlier. Get after them soon, before they set. There are no
toxicity warnings on the dye, but treat it with respect and assume it is poisonous just in case.
7) Finishing. After the parts are thoroughly dry, apply
three coats of very thin (50-70% thinner) dope. The first coat
should soak into the wood and sets the dye so it won't come
loose. Apply a second coat without sanding and allow the
parts to dry completely. The usual "balsa fuzz" can now be
smoothed with VERY fine sandpaper, nothing more aggressive than 600 grit wet-dry that is dead worn out, finer if you
have it. Fresh sandpaper will cut into your beautiful finish, so
be sure the paper is well worn out to avoid scratches. A third
coat of dope will begin to produce some sheen in the grain
marks, and this is enough finish. You can continue to add
more dope, sanding every few coats if you want a glossier
doped finish, but the three coats are enough to assure good
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water proofing and adequate smoothness.
The resulting finish is well worth the modest extra effort,
producing a uniformity and intensity of color that rivals a good
japanese tissue finish. The color is very even, while still showing off the character and grain of the wood. The dye is extremely stable once adhered to the surface. The brush will pick
up a slight amount of dye during during the application of the
first coat of dope, but only enough to slightly discolor the dope
in your jar. Just clean the brush thoroughly after the first coat.
Un-doped dye holds up well on indoor models. You will get
water spots if un-doped dye gets wet, but it has little tendency
to bleed or come off. Once doped, it is absolutely stable, and
does not take water marks if rained on. The dye remains on
the surface of the wood, and does not penetrate into the bulk
material. It therefore adds minimal weight. In closing, I list
the following applications where dyed balsa may have advantages over other finishing methods:
1) Sheet balsa scale models.
2) Colored surfaces for all types of balsa gliders.
3) Colored sheet balsa propeller blades for indoor models. Also ribs and spars.
4) As a substitute for color dope on all-balsa 1/2 A control line models. Saves much weight.
5) Tinted balsa components for all types of FF models,
eg. gas model pylons, rudders, fuselage sides, folding propellor
blades, etc.
6) Tinted fins for high performance spacemodels.
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