Sunburst practice/test - What happened here?

[putnamm]

I had some down time in the shop this weekend (waiting for glue to dry, etc.) and decided both to test some colors and to test my skills at sunbursting. I did not attempt a sunburst on my first mandolin because I found it intimidating. But this next go-round I would like to.

I had a 48 inch long piece of 1/8" maple veneer purchased from Rockler for a long-since-forgotten project. I cut it in to eight small pieces and started with a couple of different color combinations. I'm attaching photos of what I thought ended up being the best color combo and also my best result in blending the colors. I am using Transtint dyes in alcohol and mixing them half strength. I did progress through the dyes pretty quickly--a coat of amber on the entire piece, dark walnut at the edge then vintage maple in the middle and some rubbing to blend them--all in one session.

The wood itself was already very smooth. As a "project ready" piece sold by a mass retailer, you can expect that I guess. It felt like something sanded to at least a 150/180 or even possibly a 220. So I did not sand it at all, nor to I pre-treat it with any kind of sealer, shellac, etc. Just used it as I bought it off the shelf.

I've posted a few pictures, including one with a couple areas circled. I'm wondering what happened in these areas... What do you think? My guess is that if the wood had been properly sanded through the grits by my own hand--maybe to 220 or so--it would have removed any imperfections and those blotches would not be there. I'm curious what the more experienced builders and finishers think in the hopes of preventing this on my actual instruments.

Thanks.
Mark

[rcc56]

Next time, try sanding with 220 followed by 320. You can never sand enough. Clean up with a tack cloth. Follow that with a wash coat of thin shellac. Let dry for at least 48 hours. Follow with your amber base coat. Let dry for another 48 hours. Then you can start the sunbursting process with brown. If you see any signs of blotchiness, cease and desist and let dry for another 48 hours. And always use pure grain alcohol, not denatured alcohol.

Any attempts to cut corners or hurry a finishing process will yield poor results.
Inadequate curing time is possibly the most common cause of finishing problems.
It's hard to wait between steps, but wait you must. Most of us learn this the hard way.

[putnamm]

rcc56,

Thanks very much for the helpful response. I just have a couple of follow-up questions:
- This has always confused me as a newcomer. But the thin coat of shellac goes on the bare wood before any dye or stain? Does this go for all parts of the mandolin, regardless of species of wood?
- Forgive what may be a very ignorant question... But, "pure grain alcohol?" Like booze??

Thanks again.
Mark

[rcc56]

Yes, the shellac goes on the bare wood. Only a very thin coat. You can rub it in with a lint-free piece of cloth. Thin the shellac at least 30% with Golden Grain or Everclear booze. Don't drink the booze before you start working. If you decide to have some after you've finished, that's your own business. If you do, beware of pink and purple flying elephants and little men with jackhammers.

Me, I keep the PGA on the shelf with the lacquer thinner, acetone, and other poisonous liquids.

[Timbofood]

There was a furniture restoration show on PBS years ago and the (click and clack of furniture) guys referred to that as a “Spit Coat”. I have a cabinet maker buddy who does amazing finishwork and he does that on a lot of his projects.

[amowry]

Yes, I would sand to at least 320. I would take a look at this excellent video by John Hamlett of hand rubbing a sunburst.

I don't use any sealer under dye, and the trick is to just build up the color very slowly, using a dilute dye mix. As you found in your test piece, areas of end grain absorb dye much more readily, so you need to anticipate that and apply less to those areas. If you're using figured maple on the instrument, you'll find that it is more forgiving than your test piece because the end grain areas are in a uniform pattern instead of appearing to be random, and you'll actually be trying to accentuate that end grain. Spruce is more difficult, but again, just try to build the color slowly, applying it only where it needs it. If you have an airbrush to darken any areas that wouldn't take dye as well (particularly the recurve area on a spruce top), that can go a long way toward evening up a sunburst. Or, you can mix a stronger solution of dye at the end and (again) apply it only where it needs it.

I use denatured alcohol, but good ventilation is recommended, as with any solvent.

[amowry]

I forgot, I made a video a while ago too It's not as detailed as John's, but you can see how I build up the color very gradually, starting at the edge and working inward, blending frequently.

[putnamm]

Andrew, thank you. I actually found and watched your video multiple times before doing my test pieces. Very helpful.
I want to try the grain alcohol to see what differences there might be. But having seen the instruments on your site if you're using DNA then maybe the problem is more with prep and technique than the solution. But I'm up for trying everything until I find something that works for me!

[amowry]

I haven't noticed any difference between DNA and EverClear, having used both. I think it's just that EverClear is less toxic, which is a consideration if you're breathing it all day.

[rcc56]

Denatured alcohol can cause problems with aniline dyes, shellac, and nitrocellulose lacquer. These materials and violin-makers' oil varnish are the only things that I use. I have had problems with drying, cloudiness, and color changes. Other folks I know have had similar experiences. Switching to PGA solved the problems.

Denatured may be fine with things like Trans-Tint and Tru-Oil, but I am not qualified to say anything about materials I have not used.

[amowry]

Yes, I should have clarified, I use TransTint and haven’t had any problems with using denatured with that. For mixing shellac I use EverClear.

[Greg Mirken]

When I spray the first coat of a sunburst, usually a gold-yellow, I use about a 50/50 mixture of my French Polish preparation I have on hand and pure alcohol into which I add the color. This accomplishes the same thing as a shellac wash coat before coloring, but saves a little time. Then a hand-applied burst goes on more evenly.
Regarding alcohol, here in CA it's not possible to buy Everclear (protecting the wine industry maybe?) so in the past I had folks bring me some from out of state, or I put up with the nasty paint store denatured alcohol. Recently I discovered Quality Chemical ethanol on Amazon. This is pure ethanol to which they have added a bittering agent to make it undrinkable (which must have about the same BP as ethanol so it can't be distilled out). Naturally as soon as I got it I tasted it. Pretty awful. But it smells like a doctor's office, not an organic chem lab.

[Marty Jacobson]

All good points.
What you are seeing there is that the wood was soaked with wood/dye. As it dried out, the capillary action of the maple wood wicked the dye back out onto the surface of the wood. This is quite common, unavoidable with maple, really, especially soft maple like the stuff you're working with.
With a damp, nearly-dry pad, you can now use some water or alcohol to blend that dye around and get it evened back out. It's almost like burnishing with a nearly-dry pad, just enough water and/or alcohol to let you blend the color that is on the surface around without re-saturating those pores and having this happen all over again.

Half strength trans-tint? That's pretty stout. I usually do 3-5 drops in a weigh boat with a half ounce or so of alcohol or water.

Another trick is to saturate the maple with water first - that way, the tubes in the wood are already full of water, and you get less "wick-back" like the stuff you're indicating.

[sunburst]

FWIW, I sand the wood thoroughly, but only to 220 grit. I rub dyes directly on the wood with no sealer until after the staining. I use dyes dissolved in alcohol.
Parts of the wood where the grain is oriented to expose more end grain at the surface can get darker and make those dark blotches that you have there. When we see those developing we must avoid applying dyes to those areas and concentrate on other, lighter areas. Using dyes that are fairly dilute and rubbing them on repeatedly to build color helps the process to be more gradual and controllable, and darker areas are more easily avoided.
What you are doing is the right thing to do: practice on scrap.

General things to know:
-Keep the wood wet or at least damp (but not too wet, that causes other problems). I start with dilute amber/yellow dye over the whole surface and while that is still wet/damp continue with other colors. If things dry out, I wet the wood with alcohjol before proceeding.
-Once again, dilute the dyes so the process is more gradual and controllable.
-It sure helps to be at least competent using an airbrush to touch up the 'burst after rubbing. It is not always needed but when it is it can make the difference between a so-so 'burst and a good one.

BTW, I did not read all of the responses here before typing this, so if there is redundant info just ignore this post. If there is contradictory info it just shows that there are many ways to do nearly everything in luthery.

[putnamm]

Thanks again everyone for the great input. This has been very educational. I'm using multiple sample pieces to test your various suggestions.

My biggest point of confusion is the seemingly universal recommendation to notice darkening areas (end grain areas) and avoid them.

First, these areas can be very small or very close together. I am applying the dye with a small ball of clean, lint free rag. Avoiding or dying between these areas would require something like a Q-tip--or smaller--and would be very, very meticulous work. Almost like painting a model or something. Am I understanding correctly?

Second, all the videos I watch of builders applying sunburst finishes...they just seem to go to town. Fairly rapid application. Switching frequently and quickly between colors. Maybe a bit of blending here and there...but the whole process doesn't appear to take that long. These are very experienced and knowledgable builders. So I assume they just intuit, naturally where to and not to apply dye. Or perhaps the wood they are using is so fine it lacks any kind of imperfections. Is that about right?

I am not calling in to question anyone's suggestions. You are all much more experienced than me. Just trying to understand as best I can.

[rcc56]

Keep practicing. Try it both with and without a wash coat.

The reason some of us use a wash coat is to avoid uneven color absorption, but it changes the rest of the process and slows it down. And I always pay attention to Sunburst's advice on finishing-- he's a lot better at finish work than I am. He seems to build his color quite slowly, which would be a necessity if you don't use a wash coat.

But the bottom line is that you will have to keep experimenting and find the technique that works best for you. Mark your test boards so you can remember how you did each one. You can sand down the ones that are no good and use them again until you start to get the hang of it.

Oh, and beware of the implied speed of operations when watching videos. I could do a 20 minute video feature on a fret job, but it would take me 4 or 5 hours of actual time to complete the work condensed into those 20 minutes of video.

[HoGo]

...
First, these areas can be very small or very close together. I am applying the dye with a small ball of clean, lint free rag. Avoiding or dying between these areas would require something like a Q-tip--or smaller--and would be very, very meticulous work. Almost like painting a model or something. Am I understanding correctly?

Second, all the videos I watch of builders applying sunburst finishes...they just seem to go to town. Fairly rapid application. Switching frequently and quickly between colors. Maybe a bit of blending here and there...but the whole process doesn't appear to take that long. These are very experienced and knowledgable builders. So I assume they just intuit, naturally where to and not to apply dye. Or perhaps the wood they are using is so fine it lacks any kind of imperfections. Is that about right?

You should notice that most of the videos are of sunbursting hardwood, especially curly maple. That is a breeze to do compared to carved spruce top (even flat top spruce is incomparable to carved). CUrly maple is so simple because the curl causes waves of runout all ovet the piece that will necessarily show unevenness (that accents the figure) but on plain staight grained spruce any streak stands out as sore thumb. You should look for the John Hamlett video of sunbursting A4 top. he moves quickly because he uses alcohol dyes and he uses q-tips in some areas as well. You should remember you don't want to apply streak of dark color with crisp edge or if that happens you MUST not leave it dry before it is blended - with alcohol dyes you have seconds to change the pad to lighter color or clear alcohol pad and blend it.
You can also cheat and apply the stain using airbrush that gives slightly different result as the stain is typically not as deep in the wood as in rubed burst. I sometimes used cross of these two and applied color with airbrush but immediately rubbed/blended it with alcohol pads. You can get almost perfect rubbed sunburst with this on spruce. I think I did it on this one:

[Rob Roy]

To echo what the experts have already said:
• That veneer felt smooth but wasn't sanded enough in the areas that came up dark. If you wet the wood with water or naptha, you'll see those areas before applying dye. This becomes more important when dyeing curved surfaces carved out of solid wood because grain angles change. Roll cut veneer will behave more like consistent flat grain.
• Spruce is going to take dye differently than maple. It has a tendency to come out splotchy no matter how much you sand IME. This is why some resort to a wash coat of shellac first. I do a light application of Super Blonde shellac, then smooth it with 300 grit before applying color. With my limited skill, I find it gives me a smoother base to move the color around with the pad. I don't find it necessary to do this with maple.
• The reason some of the pros in the videos move so fast is because modern dyes soak in quickly and are largely permanent. Having lots of rags on hand and dish of your clear base medium handy for softening/blending is helpful for me. Water-based tints are the hardest to control for me as they soak in really fast. I only use transtint dyes in a solvent medium. I also cut it with some retarder I have on hand for finishing to give me more time for blending.
• As mentioned here by some, getting really dark with hand-rubbed sunbursting is tricky. If you want to go all the way to opaque dark brown around the edges, that last, darkest part is easier done with a gun. I learned this from a guy who finished for Gibson for years.

[sblock]

When I spray the first coat of a sunburst, usually a gold-yellow, I use about a 50/50 mixture of my French Polish preparation I have on hand and pure alcohol into which I add the color. This accomplishes the same thing as a shellac wash coat before coloring, but saves a little time. Then a hand-applied burst goes on more evenly.
Regarding alcohol, here in CA it's not possible to buy Everclear (protecting the wine industry maybe?) so in the past I had folks bring me some from out of state, or I put up with the nasty paint store denatured alcohol. Recently I discovered Quality Chemical ethanol on Amazon. This is pure ethanol to which they have added a bittering agent to make it undrinkable (which must have about the same BP as ethanol so it can't be distilled out). Naturally as soon as I got it I tasted it. Pretty awful. But it smells like a doctor's office, not an organic chem lab.

+1. This is absolutely correct. You can't buy overproof (high purity) alcohol (ethanol, that is) in certain states, like California. They do sell a watered-down version of Everclear in California, but it's only around 150 proof, not 200 proof. And the most common forms of "denatured alcohol" that are widely available, like those found in paint and hardware stores, are adulterated with a variety of -- often unspecified -- organic compounds, like methanol, acetaldehyde, pyridine, and so on. These organic compounds have different vapor pressures and different chemical reactivities, and can lead to all manner of undesirable side effects when finishing instruments.

Some forms of denatured alcohol, however, are rendered unfit to drink by simply adding a tiny amount of "bittering agent", like denatonium chloride (DC), which is just about the bitterest substance known to mankind! These particular versions of denatured alcohol don't contain methanol, acetaldehyde, and other stuff, which are usually added at much higher concentrations. The amount of DC added is so small that it doesn't tend to affect the chemical properties of the ethanol.

So, if you can't buy 200-proof Everclear (or similar overproof alcohol) and don't have access to pure, analytical-grade ethanol, of the type that might be found in a chemistry or biology lab, then a great solution is to get denatured alcohol that only has denatonium chloride, and not these other adulterants. This is available for purchase online, as Greg M has found. I don't recommend tastng it, though!

[HoGo]

So, if you can't buy 200-proof Everclear (or similar overproof alcohol) and don't have access to pure, analytical-grade ethanol, of the type that might be found in a chemistry or biology lab, then a great solution is to get denatured alcohol that only has denatonium chloride, and not these other adulterants. This is available for purchase online, as Greg M has found. I don't recommend tastng it, though!

I buy alcohol for stackfree fireplaces, it is 99.98% ethanol (200 proof?) and only tiny amount of added denatonium benzoate. It costs just under 2 EUR per liter bottle. I once put my finger in mouth 15 minutes after I stopped FP session and that was so bitter taste I will remember for life...

[putnamm]

I appreciate all the input. I'm still going at it...but it's really frustrating. Trying lots of different things but also having to take breaks so I don't get discouraged.

For a change I think I'm going to also get testing on some spare spruce I have lying around. I understand spruce is more difficult to work with, but after about a week of working with the maple I need a change.

[putnamm]

This one was sanded to 320 and wiped with tack cloth. Finest and smoothest piece I had, and it ended up with the most blotches. Argh!

[Bill McCall]

Gives you more respect for the talent of some folks, doesn’t it?

You’re learning that it takes more than 2 hours to learn. Cut yourself some slack, it’s hard.

And you can’t be born full grown

[sunburst]

Observations: Bear in mind I'm only looking at an internet photo here.

-Looks like it is not thoroughly sanded. To thoroughly sand we must first sand with a course enough grit to remove all marks from whatever tool established the surface; plane, jointer, whatever. That includes sub-surface damage because any tool causes some compression of the wood surface that goes into the wood at least a little. The sharper the tool the less sub-surface damage, but it is always there. I often start with 80 grit and sometimes 60 grit. As we continue through finer grits we must once again remove sub-surface damage left by the preceding grit all the way to 220. I raise the grain after 120 grit (wet the wood and let it dry) and again after 220 grit. I almost always find leftover scratches from earlier grits when I do that. After raising the grain I give a quick rub with 220 or 320 to remove the 'fuzz' and the wood is ready for staining.
Subsurface damage that is not sanded away leaves blotches that are lighter than the rest of the surface rather than darker. Compressed wood does not 'take the stain' well.

-Looks like it was too wet and perhaps the dyes were diluted too much.

[putnamm]

Thanks. I'm using half-strength TransTint in pure grain alcohol. I'm referring to the "TransTint For Luthiers" PDF found at the Homestead Finishing Products website, which recommends a full strength mix of 1tsp of dye for 6oz of alcohol. So I used 1/2 tsp in 6 oz.

It's possible I got it too wet. I dip the rag in the dye then blot a couple times on a paper towel. But maybe I need to blot more.

This piece was sanded starting with 80 grit then 100, 120, 150, 180, 220 and 320. I used an orbital sander with vacuum attached, then wiped with a tack cloth. I did not raise the grain at all. Didn't think of that.