ctanzio

Wowza! Work of art...

Lovely varnish work on the scroll.

Afterlength needs to be long enough to not overly restrict the rocking motion of the bridge in response to the strings, but not so long that the spring mass system of the tailpiece and afterlength starts to affect the bridge motion in odd ways. If your viola has good tone and response, do not mess with success. If you need a starting point to experiment, anything Manfio says about violas is a good starting point.

A violin bridge can be roughly broken down into two main functions: structural and acoustic. The structural function requires it to hold up the strings in a stable fashion without damaging the violin body or the strings, and enable the player to comfortably activate the strings. There is a lot of information on standard practice for dimensions and material to achieve this. Stay within the standard range for these dimensions and you will be fine. The acoustic function practice is more unsettled. But a basic understanding of how string energy is transmitted to the body can help you separate the woo from the science. Bridges made within the range of standard practice have a fundamental rocking frequency of between 2500Hz to 3000Hz. Notes played well below that frequency have the energy transferred to the body almost "unchanged". Notes played around that frequency have the energy increasingly "amplified". Notes played above that frequency are increasingly "damped" as the frequency increases. This behavior gives rise the observation of a "bridge hill" in response spectrum plots. You can dop a search on this term if you are unfamiliar with it. Playing with dimensions such as the kidney and heart size, waist thickness and bridge thickness are used to adjust the rocking frequency. Unless you do something extreme to dramatically lower the rocking frequency, and compromise the structural integrity of the bridge, the best you can do is influence the upper bands of the frequency response. Moreover, if the violin body is lacking in upper band response, there isn't much you can do to improve the sound by playing with the bridge. Hope that gives you some ideas for future experiments.

Interesting results and well done. Thanks.

Think of the term "French Polish" as a technique for adding the thinnest of layers of spirit varnish to a surface. One can use the technique to apply multiple layers to finish the wood work with a full spirit varnish, or one can use the technique to apply a thin, protective coat to an existing varnish, spirit or oil.

Just as a general observation: spirit varnishes tend to stick to anything while oil varnishes tend to need a "rough" surface to adhere to. Another way of putting it: I can polish an oil varnish with spirit with little prep other than making sure the existing varnish is clean. If I put oil over spirit (and even other oil if the varnish is especially "fat" (high percentage linseed oil) I want to make sure the surface is deglossed.

Since saffron was mentioned here is a link to a short discussion from this forum: TLDR: It can give a glow that varies from orange gold to brilliant yellow. Light fastness is a major issue. Use one of the modern dyes to achieve the same effect.

For touch up of existing varnish, those distinctions have no relevance. Typically, one is trying to match color and finish (gloss) of the existing varnish and perhaps fill in scratches or cracks. Any varnish that does this is good regardless of its designation as primer, coating or color.

There are two challenges to using spirit varnish for "touch up". 1. It dries rapidly which makes blending variations in color difficult. 2. It will dissolve existing layers of spirit varnish resulting in an uneven finish at the touch up spots. Touch up with spirit varnish is a special skill set that takes a lot of practice to master. In terms of the different products you listed, any would do if you can match the gloss and color of the existing varnish you are trying to touch up.

Great. Another fiddle tune I want to learn. Why are you feeding my addiction? On a serious note, I am amazed at the sheer number of tunes some of these fiddlers can pull out of their bows on a moments notice. I also notice that many, if not most, place the chin well on the bass side of the fiddle and bow mostly downwards. I guess it is a better hold for long playing sessions in noisy pubs?

After filtering or just letting it stand for a few days, it looks like clear water. I would pad it onto the surface then let dry. Repeat one or two times until I got a consistent haze. The degree of application to fill the pores is just anecdotal. I found a way to get repeatable results, but it might be over kill. It is possible a single, gentle pass with the solution is all that is needed. My goal was to get a ground that allowed a colored varnish to flow onto the surface with a consistent (non-streaky or splotchy) color and secure adhesion. I experimented with burnishing the hazy coat with a clean rag until the wood was just visible, but I cannot point to any advantage or disadvantage to doing this for the final finish. I do not use slaked PoP filler anymore. A simple diluted shellac pass does everything I want as a filler, surface prep for oil finish, or to add a little color as the mood suits. I am not a high-end maker so I cannot comment on tonal effects of the various grounds. Now-a-days I refinish/repair old wooden objects in between dancing, tennis and sipping fine bourbons. I was once tempted to use bourbon as a ground, but I quickly realized that would a horrible waste of a good spirit.

Calcium carbonate is very soluble in water that is saturated with carbon dioxide, where it forms calcium bicarbonate. The bicarbonate does not exist in a solid form. As the water evaporates, it solidifies back into calcium carbonate. I think it might be dependent on the pH of the water. I would need to refresh my memory on it. People who live in areas with "hard" water are very familiar with this reaction. Every few months I have to scrub the carbonate scale off toilets and water spigots in my Florida house. As a comparison, calcium sulfate (slaked pop) will dissolve ~100 times more chemical in "pure" water than calcium carbonate. So simply trying to dissolve the carbonate into water is not going to work very well at all. But if you saturate the water with carbon dioxide, you should be able to dissolve about ~100 times more carbonate than the sulfate. So I am thinking there should be a way to very effectively precipitate calcium carbonate onto a wood surface. I do not recall the carbonate/acid reaction sequence, but I would suspect you would end up with elemental calcium at the end with an incompatible refractive index. Is there a reason you think the carbonate would make a better filler than the sulfate? I would have to take a closer look at the chemical properties of the two compounds to see if one has any advantage over.

Two observations on recent posts about PoP: 1. There is no reason to extensively stir the PoP if you use my PoP solution method. Calcium sulfate has a low but useable solubility in water. You only need enough PoP to create a saturated solution. This takes mere minutes of vigorous shaking with small amounts of PoP added to the water until no more will dissolve. Applied as a solution, there is no concern about the mineral crystal size. The solution seeps into the grain, evaporates, and causes a crystal structure to grow to fill the voids. A pint size mason jar creates enough saturated solution for many projects. A 5 gallon pail might be enough for a 40 foot sail boat. 2. If you slake the sludge, let it dry then grind it up to mix with varnish, then the size to the mineral particles becomes a concern. The mineral tends becomes more of a surface coating and the varnish acts more like the grain sealer. At this point, I would consider the effort more work for little effect. Just rub a teensy bit of oil varnish into the wood as the ground/sealer and skip the PoP step altogether.

For mineral grounds, there are at least three important properties to consider: 1. Transparency to visible light. Do not be fooled by the solid white or gray appearance of ground minerals. The roughness of the surface causes the light to disperse giving the white appearance. Bentonite is a type of clay if memory serves me correctly. I doubt it is very light transparent. If a mineral is transparent to visible light, the hazy appearance is corrected by... 2. Refractive index that matches the varnish. For most varnishes used in violin refinishing, this is around 1.53 or so. It just has to be "close". It does not have to match exactly. The varnish fills in any microscopic roughness of the mineral structure and eliminates the dispersion of the light, restoring the transparency to the eye. Fully slaked plaster of paris, the dihydrate of calcium sulfate, has an ideal refractive index for most oil and spirit varnishes. 3. Resistance to water absorption. Slaked PoP has low but non-trivial water absorption. But this is a problem only when the material is under stress. It will cause the mineral structure to undergo creep failure. Make sure the PoP application is thoroughly dry and then the varnish should sufficiently protect the mineral against water absorption. Bentonite might be highly water absorbent and expand in humid conditions. Double check. If true, then I would suggest you avoid it. PoP Preparation I (maybe mistakenly) recall Hargraves PoP prep and application as being rather fussy. I suggest the following simple method. Get a large glass jar with lid. Fill with warm water from your tap. Add a tablespoon of PoP, cap, then shake vigorously. Let stand so undissolved slaked PoP settles to the bottom. The water should turn mostly clear. Repeat adding, shaking and settling until you have an obvious layer of undissolved PoP on the bottom of the jar. Paper filter the liquid into another clean jar and dispose of the sludge. The filtered water is your mineral ground solution. Dampen a clean rag or paper towel with the solution and gently dab/ wipe the wood surface until it is evenly moist. The water should evaporate rapidly leaving behind a pronounced white haze. This is crystalline calcium sulfate that will easily fill the smallest grain defects found in wood. You might have to repeat the application to get a uniform haze. You might want to lightly predampen the bare wood to raise any grain hairs and gently scrape it smooth before applying the PoP mixture. It depends a lot on how you finished the bare wood. If fine scraping was your last step, you might be able to skip this step. If you used a sanding method, odds are high even the modest amount of water applied with the PoP will raise some hairs. You can use a hair dryer on low setting to dry the PoP application. I gently wipe the dry surface with a clean cloth to remove any obvious "dust" that might have accumulated. When you apply your first coat of varnish, the wood surface will miraculously transform from a white haze to sharp, clear grain.