"crocodile" finish

[astrid]

I've got an old vienese regulator clock where the finish looks like crocodile skin,(I mean the shellac has separated in 2-3 cm patches)
I paid about $120 bucks in belgium for it and it goes)
I dont intend to refinish it as this is its patina.
but can anyone suggest what causes this,?
heat?

Astrid

[echnidna]

It must have been sealed with something prior to the shellac.
The sealer has continued to dry out and shrink long after the shellac dried solid.

There are several methods that can be used to simulate the crack(le) finish

[astrid]

thats what usually springs to mind, but this is old and isnt crackled, more like some agent has made the original surface slowly pull apart.
to be poetic, like islands of thick shellac skimmed over with new but a long time ago, never seen anything quite like it.
was wondering if hung over a really hot fire place would do it.
Its quite lovely and unique and you wouldnt want to strip it off.
just puzzled re the cause
as i said i bought it in belgium cold winters and hot stoves

Astrid

[Tonyz]

off the suject but years ago I had an original mini cooper we decided to repaint all was going well till the roof was done a seperate color. enamel and lacquer are not combatable. from a distance though looked like a white vynil roof.

[addo]

Like Tony, I've had the "gator skin" finish accident. In my case, an acrylic basecoat with 2K polyurethane overspray 24 hours later.

You might get the clock's finish by using a traditional oil varnish first (like some violin finishes), then a wipe with shellac and lacquer overspray.

Regards, Adam.

[astrid]

yes,
but this is not the case in this case
astrid

[jerryc]

I'm taking a guess as to the cause of the crocodiling which is not that unusual in finishes was a combination of heat and age. I had a locker door crocodile on my yacht when my wife got a little over enthusiastic and put on too much shellac in one go. Locker was near companionway and heat of the sun crocodiled the door.

We cured our problem by using a method I found in an old English finishers book. The method was to use a "pullover" with a rubber charged with meth. It's done by a light charge of shellac rubbed over at speed. Hard to explain but it's a combination of meth and burnishing.

I know you don't want to change the clock's appearance but the book did say that using this method kept the original patina since no dust or grease was removed and no new shellac added. Incidently the book says the same method can be applied even to a lacquer finished item providing the solvent is the same as originally used. Must say I haven't tried it on lacquer.

Jerry

[astrid]

thanks jerry,
what puzzles me is that these clocks were still factory made and i would have thought that they would have known about letting stuff dry.
the shellac island are really quite thick compaired to tha channels in between.
i's very odd.
just one of those wonderfull anomalies about finishes i guess.

Astrid

[durwood]

This effect can be achieved in various finishes and as mentioned here by some they got the effect by either applying too much material or applying the wrong finish over another.

You can do it easily by doing one thing and that is applying too much of a coating too quickly. Doesn't matter what the finish some just do it easier than others. If you find this effect and you look close you will see the cracked finish has a good deal of thickness to it.

The reason instructions quote number of coats and drying times is for this reason in most cases.

If you exceed the amount of material far past the recommended thickness you are risking this happening. One of the main reasons for stripping paint is to avoid excess film build. In a Motor vehicle the rule is after the 3rd respray you should strip the paint back to bare metal if you don't the film build is so thick that the total build can easily crack. New paint equals about 3 thousands of an inch after it reaches 10 thou repainting become a gamble. If you want to do a 1st class job it will probably fail so if you want to do it properly you must start again. (or risk the new finish cracking and then you have to also strip it as well as the previous coats)

Old paint drys out and eventually the additives in it to make it flexable enough to expand and contract are lost if there is a high build it will eventually crack. Most products are not made with the intention that thay stay around for hundreds of years.

First step is just called cracking/splitting then it becomes "crows feet" ( cracks radiate out from center) then it become crocodiling or aligatoring ( depending where you come from.)

Usually it can take years for this to happen but if the build is excessive it will happen quicker and it can happen in minutes if you mix different products or really pile on the coats fast in a short time.

I did have a sample I kept for years which a student did by putting 30 plus coats of acrylic lacquer over metal flake in one afternoon it had cracks over 10mm all over the panel next day.