Why does varnish crackle?

March 25, 2011 at 05:54 PM ·

 There are several potential reasons. One is a violation of the fat-over-lean rule, where a harder varnish is on top of a soft one. Think thin ice on a lake, and how it breaks up as the water beneath it moves. This often happens when someone puts a harder over-varnish on an old violin in the process of retouching or polishing. The most common version of this is a small ladder or net like pattern that's just on the surface and barely visible, but sometimes it can look like the defective varnish version.

Another cause is natural degradation of the varnish, particularly but not only from contact with skin. This comes under the patina heading, and can be considered really desirable if it's attractive. Usually this type is small and a little pillowy looking.

 A third cause is a varnish-making mistake. For instance, some varnishes based on rosin can shrink a lot over time and break up in big patches that look like mud flats.

These all look different, and some are considered more desirable than others.

There's another type that's not really a crackle, often seen on old English violins. They used a varnish with driers that dried from the top down. After a solid skin formed on top, subsequent drying and shrinking of what was underneath caused the skin to gather up in sort of a reverse crackle. This can be really cool looking, and usually is very strong, over the entire instrument. It's most common on dark red English instruments because the red varnish is always quite thick.

March 25, 2011 at 11:05 PM ·

I knew a cellist with an old English cello with that crackle finish. It was always a talking point for new members of the section.

March 26, 2011 at 03:44 PM ·

 does any luither know whether the crack varnish has an effect on the tone as well as the sound on their instruments :)

Crack varnish always make me very interested in the way it looks :)

March 26, 2011 at 03:51 PM ·

Everyone cracks up when they hear the sound of my cracked varnish instrument ... But it drives me crackers.

March 26, 2011 at 04:48 PM ·

There is another type of cracking of the varnish in newer instruments, often in cheaper instruments. Hermann Janzen showed me this once ( on someone else's instrument).It is harder to see, but with oblique light you see numerous fine parallel cracks under the surface of the varnish. This is due to shrinking of the wood and happens most when improperly dried or relatively new  wood is used. I don't know if this can also happen in a well built violin if there is a major change in humidity, but imagine it possible could .

BTW fine cracking of paint or varnish in paintings is called craquelure:

http://en.wikipedia.org/wiki/Craquelure

The pattern sometimes looks similar to the cracked varnish on old violins.

March 26, 2011 at 06:17 PM ·

 Peter, you mean you can actually hear the crackling of the varnish on your instrument? 

March 26, 2011 at 06:49 PM ·

 Thanks for the responses.

Some violins have to varying degrees, a shiny layer which I've told is French polish.  Though Michael mentions some forms of crackling are aesthetically pleasing, isFrench polish used to minimize crackling?  

The violins with less French polish appear to have a thinner "skin" that I intuitively think allows the instrument to resonate more freely.  But is that a fact?

I've seen expensive new instruments with a liberal does of French wax, as well as old violins. And student violins look almost plastic!

Jason

March 26, 2011 at 06:58 PM ·

my violin has those 'crack varnish' i thought its called patch mark.

modesty aside, this violin of mine is the sweetest and way  easy to play. Don't know though if it is because of that varnish or not.

March 27, 2011 at 08:17 AM ·

"Peter, you mean you can actually hear the crackling of the varnish on your instrument? "

Trevor

It competes with my open E and produces a wolf!! I've cured it by putting on a D'Arrio Kaplan non whistling E. All the young ladies tell me I'm better behaved now as they don't hear any wolf whistles ... I now have to use other techniques to be able to adjust their G strings ...

But the cracked varnish still cracks up when it hears me playing!!

March 27, 2011 at 12:43 PM ·

In fact I'm not sure the wolf E is completely cured and the Kapaln E has a poor sound on my fiddle AND it has made the A sound dreadful. Damned instrument.

March 27, 2011 at 09:41 PM ·

Michael: "...a harder varnish is on top of a soft one. Think thin ice on a lake, and how it breaks up as the water beneath it moves..."

Hmmm...did varnish crackle suggest continental shift long before science proved it? ;-)

March 28, 2011 at 02:22 AM ·

In oil painting, we often use a medium consisting of fast drying turpentine and slow drying linseed oil. When the mixture is too lean, i.e. more turpentine than linseed oil, the resulting painting has spider web cracks on its surface after a period of time. Some find it cool, since  the picture appears to be older than it is. Can this be another reason why cracks appear on  varnish in violins?  The luthier could have used a mixed solvent for his vanish and inadvertently used one that is too lean?