Here are some progression shots of a German waldzither that I'm working on for a customer. After a bit of cleaning I've filled these two top cracks with new spruce. The new wood is much whiter than the original wood but after a bit of color, varnish, and a few years of time it'll be much closer to the same color.
This hairline crack along the fretboard was also filled with new spruce, too.
As you can see, the original finish (after cleaning) still has some decent gloss, but is marred by a ton of scratches, scuffs, and grime.
As is the back!
Here I've been polishing up the frets.
The black lacquered neck is also riddled with use wear.
Here are those filled cracks after a touch of amber color and some new varnish. As you can see, they're much closer in color than before, but like most fill repairs, they won't match perfectly without a good sanding and refinishing of the area.
They're much less visible in this photo with less glare (due to the storm clouds moving in).
Here you can see my touchup on the sides: I've minimized what could be minimized, removed all the scuffs, and applied color to match in the worst of the nicks and scratches. After that I've top-coated (very thinly) to seal it all and bring back some shine to this finish.
Here's the other side, which was worse off -- but still much improved from the photos above.
Here you can see it better: only big gouges that've chipped at the old finish really stand out at all and then really only at certain angles.
The fretboard has improved dramatically: the rosewood is now cleaned up and conditioned and has a deep, attractive color.
Soundhole: the ebony was starting to dry-crack in various places around this inlay. I've filled the cracks for stability and applied a thin layer of varnish to seal, which also brings out the color better, too.
I've managed to rub a bunch of glue down into areas where the binding and purfling was showing any gaps and have removed any movement. Now, after a nice cleaning and a thin coat of varnish, the colors really pop out.
The crack along the neck is looking better, too.
I've also started to touch up (a bit) areas where the black lacquer had been rubbed away and was showing wood. After a couple coats of varnish the touchup will blend better with the original.
As you can see, I haven't redone every little bit, but left it looking as original as possible (but still desirable).
Here's the back, looking a little muted because of the cloud cover, but really overall much much better.
Here's the back at a different angle so you can see some of the remaining wear marks.