Laser Etched & Colored Soundboard - Made at Techshop

In this instructable I'll explain how I designed, etched and colored the custom artwork on the soundboard of my carbon fiber acoustic guitar project, part of a special event at Techshop. This top was designed with my own digital artwork, engraved with a laser, then colored with dye. This was my first, and maybe only, time making a guitar, so I decided to go all-out.

Painting guitars can be a bad idea, as normal paints can kill the sound of the instrument. But I was inspired by the artwork of Peter Cree, a guitar builder who uses colored lacquer and shellac to "paint" full-on artwork on acoustic guitars. He claims that his hand-painted finishing method produces a finish that is 2-4 microns thick - better than many commercial guitars. I couldn't find details of Peter's method, and I have no idea how to measure microns on my finish, but I decided to try and find some way to do something similar.

Disclaimer:

Before I get started, I want to say that I am NOT an expert luthier (stringed instrument maker). I tried my best to do my own research and follow the plans for my guitar design, but only time will tell if I was successful. If you choose to make your own guitar, please do your own research using professional guides. There are several amateur luthier communities online, as well as good books. I personally used How to build your own Acoustic Guitar - by Jonathan Kinkead, found at my local library.

Many people have found out the hard way that painting or staining a guitar top can severely alter or even destroy the sound of the instrument. Spray paint, acrylic paint, oil paint, stain, etc… - all of these add weight to the soundboard and have binding agents in them that can limit the flexibility of the wood and deaden the sound.

Because of this problem, traditional luthiers are loathe to use too much pigment on the soundboard. Complex artwork is usually limited to electric guitars, where the acoustics of the wood matter much less.  But I wanted to find a way with my acoustic.

My method

Pictured is the first Peter Cree guitar I saw when researching online. You can see more of his work on his website.

I couldn't find details about Peter's methods for coloring his lacquer / shellac, so I tried my best to find my own solution. I needed a lightweight, powerful method of coloring either the wood or the finish. I found the aniline dye offered by Luthiers Mercantile International, where I'd already bought all my other guitar gear. 

I discovered that by using the aniline dye, combined with the laser cutter, I was able to color very neat images directly on the wood's surface. Usually, when dye hits wood, the color explodes in all directions following the wood grain. So dye alone would have led to a very messy "impressionist" style of artwork. But by using the laser cutter, I broke the wood fibers - which stopped the color from flowing everywhere. Just look at the pictures to see the difference between using dye with and with out the laser lines.

As far as adding extra bulk or binders, I've found aniline dye is concentrated stuff, just a small pinch of each color made 2-3 times more dye than I needed for the whole guitar. I chose the alcohol soluble version (water based is also available) so that I could dye the wood directly, and the colors wouldn't run when I put on my water based "lacquer."

Another advantage of alcohol based dye is that then alcohol evaporates in seconds, allowing me to work quickly and leaving behind no extra bulk.

I tested the sound of the guitar before and after coloring - knocking on the top to hear the simple tone and volume, and tuning the strings. I could not hear any difference based on the colors alone. Though of course the tone did change a bit after applying the clear coat - as it would after any finish.

Materials used

• Western red cedar soundboard, planed to 2.5mm thick - $40
• Aniline powdered dye (alcohol version) - $5.75 per color, $22 for 6 color set (red, yellow, blue, brown, amber, black)
• Mixtol white (20ml) - $5.30 (there was no white aniline dye, but I needed something for the dandelion puffs)
• KTM-9 gloss, 8oz - $15.25 - a water based clear coat
• Denatured alcohol - $7.00
• Painters tape

Tools used

• Epilog 60 watt laser
• Paint brushes - variety of sizes / shapes
• Containers for mixed dye, alcohol rinse

Software used

• Adobe Illustrator

Notes on materials

• The soundboard, aniline dye and KTM-9 finish were bought from Luthiers Mercantile International
• Soft woods, especially spruce, western red cedar and redwood are the most common guitar soundboards. Hardwoods are sometimes used, but can be more difficult to get a good tone. Though one person in my workshop used Paduk to make a great sounding instrument. Whatever the species, use straight-grained, knot-free lumber.
• The aniline dye used here is the alcohol soluble version. Bbecause I'm using a water based clear coat, difference in the solvent prevents the colors from running once the clear coat is applied.
• The Mixtol white is a universal pigment, soluble in water, oil and alcohol. It was bought from local art store Douglass & Sturgess. It will bleed in my finish, but I used it sparingly.
• Denatured alcohol and tape are available from any hardware store

Brainstorming

I knew I wanted my design to be based on my favorite poem - "On Work" by Kahlil Gibran. After searching through the poem for visuals to inspire my artwork, I decided on this quote…

"...But I say, not in sleep but in the overwakefulness of noontide,
That the wind speaks not more sweetly to the giant oaks than to the least of all the blades of grass;
And he alone is great who turns the voice of the wind into a song made sweeter by his own loving.

Work is love made visible."

Based on this, I came up with the name "WindSong" for the guitar, and knew I wanted a design related to wind..

I stared brainstorming my artwork by sketching some rough guitar shapes in my notebook and trying different layouts. I knew that I wanted a woman - a personification of the wind "speaking" from the poem - and some plants, the tree and grass mentioned above. In the end I couldn't find a place to use trees, and decided to change the grass to dandelions being blown away.

At first I wanted to create detailed artwork like on Peter Cree's guitars, but then scaled back my ambitions. Not only would a detailed picture be physically difficult for me to paint on a guitar top, but having never worked with wood dye before and had no idea how it would behave or how to mix the colors. So I decided to go with a very simple 2D style of art. I had the idea of making the pictures look like stained glass, chopping the board up into smaller squares.

Sizing the soundboard

Before I started drawing my artwork, I wanted to determine the exact size and shape of my soundboard - since my guitar body was hand-formed, it's slightly different than the computer model used to make it. Once I finished my CARBON FIBER GUITAR BODY, I traced the outline of the body onto some pieces of paper (actually, scraps of foam-board that I found in the trash) then scanned the tracings into Illustrator. I joined them together into an outline, then enlarged it slightly on all sides, to make room for any errors in fitting the board.

Drawing & tracing

I had a rough idea of what I wanted - an early sketch is shown in the third photo. I tried drawing the woman and flowers directly into Illustrator, but I couldn't quite get the results that I wanted. So I headed to Google image search to find something I could use for a foundation.

Here I compare the source images I used up against the final product. In the case of the woman I used the drawing that I found online to make a tracing of her facial profile and lips using the pen tool and spline tool. I made some slight adjustments to the proportions of her face after tracing. I later decided that I didn't like her original hair, so I went drew in some new hair with the spline tool.

For the dandelion I used Illustrator's "live trace" feature to directly copy the plant and seed pods. I tried dozens of different dandelion pictures, and even tried taking some pictures of dandelions around my apartment, but in the end this silhouette best matched the 2D style of the woman. But I didn't like the seed pods for the guitar - they looked messy, and I thought they would be very difficult to color, so I simplified them to a more basic shape.

Stained-glass-ifying

The final artwork doesn't look exactly like stained glass, of course, but that's what I was going for. I also liked the twisting shapes of the squares, because it made the whole picture look more windswept - in keeping with my theme. Here's how I did it.

1. Make a new layer above the finished artwork. In the new layer draw a grid of lines over the picture
2. Select all the lines, and in the Effects menu, select one of the distort & transform options - shown here is the "twist" effect. I twisted the lines until I was happy with the way they looked. Pictured is me doing a single twist, but for the final artwork I selected groups of lines and twisted them in different directions
3. Once satisfied, open the "Pathfinder" window, available under the top "Windows" menu
4. I used the pathfinder tool to cut away the extra lines outside the guitar shape. To do this, I first made a copy of the guitar shape outline - it will be consumed in the next step
5. Select the twisted lines and the new guitar shape outline, then select "Divide" from the lower left corner of the Pathfinder window.
6. There are a few stray lines outside the guitar shape that can be deleted individually, but it now has the look I wanted. Before cutting it on the laser I also rearranged some of the lines to make them easier to color, to avoid brushing in very small squares and difficult corners.

Prepare the soundboard

I prepared the soundboard by cutting it to the size of the laser cutter bed, then planed it from its original 4mm thick down to 2.6mm thick. I wanted to go a little thinner, but this planer sometimes has trouble with very thin wood, and I didn't want to risk it. A drum sander would be the ideal tool.

I saved the scraps pieces from cutting the soundboard to test my laser settings.

Test cut

I did two sets of test cuts before cutting my real soundboard. First, I found some thin plywood in the wood shop and tested my vector cuts to make sure everything was the right size and was placed correctly. Second, I used the scraps cut from the sides of my soundboard to find the perfect laser settings. I wanted to etch my image onto the surface without burning through, and I wanted to cut out the outline and sound hole without too much charring. 

I saved my test plywood soundboard, so that I could use it to practice coloring with the aniline dye before tacking my real soundboard.

Real cut

I cut my board in two passes. First, I etched the artwork onto the soundboard, then went back and cut out the body shape and sound hole. My reasoning was that if I made some sort of mistake etching the artwork, I could always turn it over and have a second try - but once the holes were cut, I was stuck with them. Here's the settings I used - determined from my last round of test cuts on actual soundboard scraps.

Artwork

   * Type: Vector
   * Speed: 70%
   * Power: 90%
   * Frequency: 500

Body & sound hole cut-out

   * Type: Vector
   * Speed: 25%
   * Power: 90%
   * Frequency: 500

Brace the soundboard

Once the soundboard was cut, I put braces on the back to reinforce it. Bracing helps the soundboard hold up under the constant tension from the strings, and also helps to shape the acoustics of the soundboard. Professional builders can spend a lot of time on the bracing - gently shaving, sanding, and tapping on the wood to hear the tone.

My bracing job was a bit MacGyvered, without any of the special clamping setup used by most builders. I copied the size and shape (scalloping) of the braces straight from the Gibson plans my guitar was based on. I tried a bit of tap-testing to listen for changes, but frankly I don't know what to listen for, so I have no idea if I got this part right.

I may post an instructable on my bracing in the future - but only after playing my guitar for a while and seeing how good my work was (or how bad :^P). In the mean time, here's a thorough video discussing top bracing. And any decent book on guitar building should also discuss bracing.

Mount the soundboard

• I spread 5 minute epoxy around the top edge of my carbon fiber body
• I centered the soundboard, making sure that the bracing wasn't touching the sides, which could deaden the sound
• I couldn't clamp on the round body of my guitar, so I taped it and turned it upside down with heavy weights on the back
• Once the glue dried, I used a file and sandpaper to shave the edges flush with the body

Prepare the wood

• Mask off all other wood components with painters tape, to protect them from dye and finish
• Sand the soundboard, start with 150 grit sandpaper, followed by 220, 320 and 400 grit sandpaper. Use a sanding block to keep the sanding level, and always sand WITH the grain, not against it.
• Scrapers can also be useful after the sandpaper, but I couldn't find my scraper, so I just used the sandpaper.
• Water based finishes will cause loose wood fibers to rise up, making a rough finish. To avoid this, slightly wet the wood between changes of sandpaper. This will allow you to knock down all the loose fibers before applying the finish - leading to a much smoother end result.

When I was sanding, I didn't yet know how important the laser lines would be for applying the dye. I almost sanded away too much, which would have let the dye flow over the laser lines. It's best not to be too aggressive here, just sand enough to get a smooth surface and knock down loose fibers.

Beware of dye dust

As I said earlier, aniline dye is powerful stuff. I strongly suggest experimenting with it before tackling the final project. I also suggest practicing in a different location than the final project, because aniline dye power can be messy stuff. Just a few invisible specks of the powder were enough to cause small starbursts of color when mixed with alcohol. When practicing on my plywood soundboard, a few flecks of blue power got onto my board and contaminated everything - see third picture.

When it came time to color my real soundboard, I moved to a totally different table just to make sure it was dye-dust free.

Mixing the dye

I didn't measure my dye out very carefully, because I thought I would need more and just made enough to practice with. It turns out I needed very little, and I liked the colors, so I just used the same dye mix for my actual soundboard. But I can try to estimate.

I filled six 2oz bottles about halfway with denatured alcohol, then scooped in roughly equal pinches of dye dust with a coffee stirrer. When making green, I put in half a scoop of yellow, then slowly added very small amounts of blue until it was the shade I wanted. I think this is when the blue dust got everywhere.

Testing & practice

I first tested my colors and brushing method on my plywood test-board. It went well - I liked the colors, and I discovered the dye-blocking effect of the laser lines. When I tried the same tests on the scrap pieces of cedar soundboard, it also went well - though the colors came out darker and redder than on the plywood.

I also discovered in my tests that it's not a good idea to use too much of the Mixol dye. I had planned to mix the white with the aniline dye to lighten certain colors (for example giving my girl's hair some highlights). But when I tested out my water-based laquer on the test-board, I discovered the white Mixol easily bled into the finish, since it's a universal colorant (mixes with water, alcohol and oil). Because of this, I limited my use of white to the dandelion puffs, and was very careful when brushing over the lacquer on my real soundboard.

Okay, time to color the real soundboard. Here's a short video of the coloring


My original plan was to color the laser lines black, then dye colors in between the lines - but I quickly adopted a different strategy based on my experiments. The laser lines made coloring in each square pretty easy - and it would have been even easier if I hadn't sanded the lines down so much. 

Coloring tips

• Don't use too much dye. Using a lot of dye will "flood" a square, causing the dye to jump the laser lines (last picture)
• To lighten a color, add more alcohol to the dye.
• To darken a color, try using more coats of dye. Most of my colors used only one coat, but the woman's brown hair and red lips needed 2-3 coats.
• The white Mixol is soluble in water, alcohol or oil - so it could bleed into my water-based finish. I used it very lightly just for the dandelion puffs.
• Use a variety of brush shapes and sizes to color in large areas. It's best to use the largest brush possible to achieve even coloring
• Very small areas and tight corners often don't need brushing - just tap the brush in the middle of the section, and the dye will automatically flow out and fill the space.
• If a square turns out blotchy or unevenly colored, quickly fill a brush with clean alcohol and rub over the area - this can help re-distribute the dye more evenly.
• Always keep the brushes wet with alcohol. They dry out quickly, causing the dye to adhere to the bristles. I kept a large cup of clean alcohol to store and rinse my brushes while working.

Traditional methods

In guitar making, the classic finishes are nitrocellulose lacquer and shellac. The lacquer is usually sprayed on, with many thin coats built up over several days. Shellac is often applied with a technique called "french polishing."


Unfortunately I don't have any experience spraying anything, or any spray equipment. And although french polishing can produce beautiful results, it takes a long time, can be fussy, and isn't as durable as lacquer. For these reasons, I went looking for another option.

Brush-on, water based "lacquer"

Reading through several luthier forums, I discovered two finishes that are gaining popularity with amateur builders - KTM-9 and STK-SV, made by a company called Grafted Coatings. I chose KTM-9.

One advantage of KTM-9 is that it's water based, which makes it very low-odor, more environmentally friendly and safer. Another advantage is that it has a slower dry time than lacquer, making it easier for a beginner to apply with a brush.

Brushing it on was pretty simple, but as always, I recommend practicing on something else before finishing the final workpiece. I practiced with my plywood practice soundboard.

Here is a guide to using KTM-9 to finish a guitar from builder Keith Rhodes, found on Luthiers Mercantile International website. His tutorial discusses finishing the BODY of a wood guitar - not the sound-board, but most of the process is the same. Just don't use wood filler on a soundboard before finishing.

Below is a description of my method. This was completed over 4 days, slowly building up a finish. From what I've read, applying too many layers in one day can slow down the overall cure time - I chose to play it safe and applied 3-4 thin coats per day.

The process

1. Use a synthetic brush. Natural fiber brushes absorb the water from the finish.
2. Load up a 1.5" wide brush with KTM-9. Dip it in the finish for several seconds, then hold up the brush until it stops dripping.
3. Use long, straight strokes to apply the finish. Don't go over the same area multiple times. If you make a mistake, just paint over the entire stroke again instead of fussing with multiple small strokes
4. Each new stroke should slightly overlap the previous stroke. Use very slow strokes to avoid making bubbles.
5. Coat the entire guitar, then let it dry ~2 hours before re-coating. Apply up to 4 coats in one day, then let it harden overnight.
6. After each round of coats, I VERY lightly sanded the surface with 600 grit sandpaper. Don't use too much force - each layer is very thin and it is very easy to sand straight through a whole day of finishing.
7. I followed this schedule over 4 days. It only takes a few minutes to brush each coat, so I worked on other projects while I waited for each coat to dry.

Tips

• Bubbles can form when brushing, and are usually caused by fast brush strokes. Try slowing down - way down. If that doesn't work, there may be some other problem - the wrong type of brush or rough patches on the wood, for example.
• After my first coat, I started thinning my KTM-9 with ~25% water. I'm not sure if that's an ideal ratio, it's just what I decided to try. This helped the finish flow easier off the brush, and mostly stopped bubbles from forming.
• If you find any any large runs, bubbles or puddles of finish after a coat has dried, you can gently sand them away, or carefully slice them flat with a sharp razor blade.

After the final layer dries, I've read it takes 2-4 weeks to fully cure and harden. I'm now 2 weeks into this process, and it has gotten noticeably harder. The first day I could easily scratch the finish with my fingernail - now my nails glide over the surface without scratching it. I'm going to go ahead and wait a full month before final sanding and polishing. I will update the instructable when that is completed.

Well, that's it! I had a lot of fun doing this project. I really liked the combination of the laser cutter and wood dye - I'm already thinking of more experiments to try using this basic dying method.