What does "varnish sinking" mean?

[9lbShellhamer]

Sorry, tried to research this to no avail.

What is "varnish sinking".

It seems to be coming up a lot lately. Does anyone have a description or pictures?

Thanks

[Dale Ludewig]

Varnish and lacquer, as well as other finishes, are basically solids dissolved in solvents. After the finish is applied, the solvents (oil, lacquer thinner, etc. ) evaporate. Depending on the finish, this can take weeks, months, or years, to finish. Usually there is a rapid gassing off soon after the finish is applied. The finish settles down somewhat. With lacquer, you usually should wait a couple of weeks after the final finish is applied before "level sanding" and buffing out. It you don't wait that long, you can level sand and buff out but the finish will continue to shrink as the solvents evaporate and what was level isn't anymore. The same thing happens with varnish, but at a slower pace.

The reason this is an issue is that no matter how carefully made the instrument is, all the surfaces, such as between binding and the surface it's applied to, aren't flush with no gaps at all. On a violin, the purfling slot, is not perfect. There are always little gaps and uneveness, although they may not look like much when everything is sitting there "raw", with no finish.

Finish levels everything out, like flooding an area in a parking lot. All the potholes are filled in and everything looks like a skating rink. But then the solvents evaporate and the potholes can be seen again. But there's some solids filling in everything. So you flood it again. Same thing. Over and over again. After there's enough solids left after the evaporation, you try to level everything by sanding without going through to bare wood. Then you start the whole process over again: flood, wait, flood, wait. Sand. Etc. At some point you stop and say "that's good". But as time passes, what little solvent may be left in the finish evaporates and the finish "sinks" into the little cracks and potholes. It's inevitable and actually gives the instrument some character. Along with the other dings and scratches.

[Ivan Kelsall]

Thanks for a good & ''understandable'' explanation Dale,
Ivan

[Tavy]

Dales reply was completely comprehensive.

I'd just add that even polymer finishes such as EnduroVar have the same issue.

The degree of sinkage will depend on the wood types as well, I'll try and take some photo's later as this stuff is interesting (in a nerdy kind of way !)

[Tavy]

Here's some photos, this is EnduroVar rather than traditional varnish, but the process is the same.

Let's start with 1 year old finish over maple, traditionally the pores in maple are so fine that we don't worry about the finish sinking in. However, if you get the camera close enough you can see where the finish is starting to dimple very slightly. Look at the edge of the light reflection to see the effect. Normally you simply cannot see this, perhaps a very slight aged look if it catches the light "just so". This level of effect I actually quite like:



Now lets try a more usual finishing blem on the same instrument... wherever there is a join between two materials, you run the risk of the finish sinking into the join and showing a line. If the join is between differing material types that expand/contract at different rates then some kind of line developing is pretty much inevitable. Here we have plastic binding next to wood. In fact there are several blems here: Finish sinking into the relatively porous mahogany, a couple of spots where the finish has either worn (hey, it's the neck, and I've been playing her!), or else I sanded too thin, and a slight line where the plastic binding meets the wood:



Finally an extreme example of very porous wood: burr walnut. This stuff is basically one big hole with a few bits of wood here and there! But that's what makes it look the way it does and why we like it. This was left for 3 weeks to harden, then any large pits in the burr not filled with finish were filled with CA before level sanding and top coating, then sanding level again and polishing. Six weeks later there's quite a lot of dimpling down into the wood - compare the ripple at the edge of the reflection to the maple photo. Again, under normal viewing it's not particularly noticeable, you really see it most when the light catches the top and the instrument is moving (which makes this stuff darn hard to photograph "still"!). For a sense of scale, those sanding scratches that I somehow managed to miss, were from 6K micromesh - for many finishes those would represent "job done". The effect in this case is somewhat akin to the checking you get in lacquer as it ages, albeit on a smaller scale:



And now I'm going to stop searching my instruments for blems lest you all get the wrong idea

[Mark Gunter]

Kudos on getting some good shots to illustrate those effects, Tavy.

[9lbShellhamer]

Awesome descriptions and pictures! Thanks!