Posts Tagged ‘coffee stain’

Finishing Sequence Part One

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Beginning of the Finish

We looked last time at the viola with the edgework incomplete, and final scraping not done.

Edgeork incomplete

Edgeork incomplete

Edgework

Here is the viola with the edgework done. Notice that the outer edges have been rounded inward to meet the edge crest, so that the junction between edge crest and purfling channel makes a clean ridge around the perimeter of the viola. This is just something I do, because I like it…as far as I know, it has no functional value. Many old master instruments have a much less clearly defined crest.

Edgework complete, back view

Edgework complete, back view

 

Edgework complete; angled view.

Edgework complete; angled view.

 

Edgework detail

Edgework detail

 

Coffee Stain and Re-smoothing

Then I wet the fiddle down with coffee, to raise the grain and add some color. One result is that my edgework all needs to be reworked with a small, sharp scraper. The other is that the whole instrument needs to be re-sanded, using 400-grit sandpaper. The water in the stain raises the grain, so that every random fiber that is not closely tied to the surface will swell, and raise up, making the whole surface very rough. So I deliberately raise the grain, and then scrape or sand off the rough surface. Using a very sharp scraper, very lightly, just “brushing away the rough stuff” is probably the best way to do this. I use a scraper for the areas where I want detailed, clean edges, and 400-grit abrasive paper for the broad surfaces. I perform this step at least twice, before moving on to the mineral ground. The result is a surprisingly light, yellow-tan color, all over. Almost just a cream-color. It will darken up nicely under varnish, though, and not glow white from under the varnish.

Come to think of it, the above photos already have the coffee stain, too. I forgot to take photos of just the edgework, I guess. So–those photos are right before I applied the mineral ground.

Mineral Ground

This is a suspension of very fine particles of gypsum…in a coffee-solution, because I still want to add more color, if I can. Other people use other minerals–finely ground mica, finely ground glass, microscopic beads of glass, clay, volcanic ash or other non-organic nano-particles. Some omit this step entirely. Roger Hargrave shared this as having had an important effect on his sound, so I have tried it, for the last several instruments, with what seem to be positive results.

I keep the solution well-stirred-up, and brush it on liberally, then rub it into the wood with my fingers, as vigorously as I can. Finally, I wipe off as much of the excess as I can, using a rag. The stuff goes on looking brown, because of the coffee, but dries to a chalky-white film. I don’t particularly want it on the wood– I want the microscopic particles to fill the pores in the wood, so that the varnish will be less likely to soak deeply into the wood, and deaden the sound of the viola.

The ground dries rapidly, leaving the whole viola a chalky-white, ugly object. I go over the dry instrument, checking everything, and scraping or sanding off all the excess ground. When I can see the grain of the wood everywhere (though dimly) through the gypsum film, I apply the sealer coat.

Mineral Ground, wet...back view

Mineral Ground, wet…back view.

 

Ground drying

The ground dried rapidly– this was only about three minutes after the above picture.

 

Mineral ground drying

And this was only about five minutes.

 

Dry Mineral ground

Here it is, dry–without the flash. In daylight this is chalk-white. See how the grain is obscured.

 

Mineral ground dry front view

And the front– you can see the excess pretty easily.

 

 excess ground

Here, you can see the excess ground in the f-holes, and along the purfling.

 

All that excess gypsum had to come off. It took a while, but I got it ready to seal:

Viola front is ready for sealer

Viola front is ready for sealer– all the excess mineral ground has been cleared away.

 

Back ready for sealer

The back, ribs and scroll have been prepared, too. All are ready for the sealer.

 

Sealer–What kind?

Different makers use different sealers:

  • Some use a very thin varnish.
  • Some use Rosin-oil (I’m not even sure what it is….)
  • Some use shellac.
  • Some use commercially available sealers.

Currently, I am using a very thin mixture of pine pitch and turpentine, with a little alcohol. The alcohol and turpentine cause the mix to penetrate deeply. The pine-pitch goes into the wood along with the solvents, and remains there. It is interesting to watch the sealer going on…the chalk-white gypsum instantly turns transparent, and effectively disappears, leaving the natural color of the wood, along with whatever staining was added.

Without adding any color to the sealer, this would leave the wood a somewhat pale color. Usually, I have been satisfied to add color later. I added a little amber color to the sealer, this time, though, because my last instrument was a little too light-colored, initially, and I didn’t like the result.

The alcohol evaporates nearly immediately, while the turpentine takes a few days to evaporate, and (I am told) it leaves a bit of residue, as well. But that is OK. Turpentine is a natural wood extract, and I don’t mind it being in the wood.

The pitch dries in the wood, locking the gypsum in place, and sealing the wood against any other substance. Again, the pine-pitch is a natural wood extract, which eventually dries hard, and I don’t mind it being in the wood. Besides, it smells nice. 🙂

Here is the viola with just the sealer. I will show the varnishing sequence in the next post.

Sealed Front

Sealed Front., using the flash.

 

Sealed viola back

And…here’s the freshly-sealed back; again, using the flash.

The wood will change color just a little as the sealer dries. But it will never go back to the dull-looking finish where the grain is obscured again. The varnish I apply will enhance, not obscure the figure in the wood…I hope. 🙂

Varnish (coming…)

I use a spirit-varnish, currently, though I have used oil varnishes in the past, and undoubtedly will again. I will start off with a yellow varnish to enhance the figure in the wood, then use darker coats to finish. I use enough coats to get the color the way I want it, including whatever shading I choose to do, then add enough clear coats to give it the depth and sparkle I want. Usually 6-8 coats, I guess. I sand lightly after virtually every coat, to reduce any bumps, sags, runs, or brush-marks, as well as looking for brush hairs or bugs, stuck in the varnish film (it happens….)

Finally I rub the surface with extremely fine abrasive (12,000-grit micro-mesh), and then polish it all over, using the dry skin of my palm, or thumbs, rubbing hard enough that the varnish gets uncomfortably hot. This takes away the “glittery” look of the fresh varnish, and leaves the glow of hand-rubbed work. Pictures in the next weblog post.

Thanks for looking.

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Progress on a 14-inch Viola

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Continuing on the 14-inch Viola

Arching and Graduation

The outside arching for the front plate is essentially complete, though there will be a lot of scraping, later on. I began the graduation (inside arching) of the front plate about the same time as I took off and “sprinted for the finish line” with the “Plowden” Guarneri-model violin (see recent posts), but all I accomplished was that the center of the plate is about the right thickness– everywhere else it was still way too thick.

So! Back to work! You can see (below) that the f-holes have been laid out and deeply incised, which allowed me to accomplish the last stage of the front arching (explained in an earlier post.) Now I need to carefully carve away the interior, until all the plate is the thickness I want it to be…which varies by region, all over the plate. I have to be very careful to check certain areas with a caliper before I begin to carve, or I may easily go too far and make the plate too thin. (Voice of sad experience….) The area around the lower ends of the f-holes are very likely victims of this error, so I try to check regularly, and avoid carving away too much in those areas, especially.

Outer arching small viola top

The outer arching of the small viola is complete, not counting the purfling channel.

 

Side view of small viola arching, before purfling and edgework.

Side view of the small viola’s arching, before purfling and edgework is done.

 

Inside arching of the small viola.

Inside arching of the small viola. The Graduation is complete. Next, I need to cut out the f-holes, and add the bass-bar. I do realize the corners are too long…I will trim them later.

 

Coffee Stain

One thing I decided on this instrument was that I should begin the coffee staining very early, so that, if there is any distortion, due to the wetting of the wood, I can correct it before the plates go on the garland. In this photo, it is hard to see how much the grain is raised, but, those wide summer grains of the Sitka Spruce are all swelled up like corduroy!

Accentuated grain lines, due to coffee stain.

Accentuated grain lines, due to coffee stain.

I will let it dry, and then gently scrape it smooth again. The issue, here, is that the summer grain swells more than the winter reeds, but when we scrape the wood, the summer reeds compress, while the winter reeds resist the blade and are cut away. The result is that the summer reeds are already raised, even before I wet it down and deliberately raise the grain, before leveling it again.

Things remaining:

When the plate is nearly perfect all over, I will finish cutting out the f-holes, and finish their edges as well as I can. I nearly always see something later that I have missed, so I just accept the fact that I will be making corrections right up until the time I begin varnishing. The same thing applies to the scroll. It will never be “perfect”, and I accept that.

I will lay out and fit the bass-bar, trying for an air-tight fit between the bass bar and the inside of the front plate. I install it using hot hide glue and clamps, but will trim it to the proper shape after the glue is dry.

After the bass-bar is fully completed, I round the inner edges of the front plate, so that it is ready to install on the garland.

Post Script:

All of the above was accomplished three weeks ago, before we left on vacation, so it should have been published then, too…but I kept thinking I would get a little more done before we left, so it simply did not happen.

We are back, and progress is once again happening, so I will post more in a day or two.

Thanks for looking.

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