Any ideas what caused this?

[RogerS]

...and perhaps more importantly, is there an easy fix? The finish is multiple coats of shellac.

 

[marcros]

I would hazard a guess at moisture if we are looking at the white ring. There is a trick with method and setting fire to it if that is the issue. Difficult to really see what is reflection from the pic

 

[Mike.S]

Any more clues - what is it, where located (much traffic) and any pets?

I'm assuming it's the pitted finish, rather than the white ring (reflection?), that's in question.

 

[RogerS]

Thanks guys.

The white ring is a reflection. I am talking about the pitting. No traffic at all and only collected from the workshop yesterday. That will teach me to insist the client spends an hour going over it with a fine toothcomb before taking it away. I have a photo taken part way through the finishing process and no sign of any pitting at all.

I too was wondering about a cat...not sure.

 

[mrpercysnodgrass]

Hi Rodger, I can think of three possible causes.
1. The wood has been bleached with hydrogen peroxide and has not been properly neutralised. Usually this would produce small pinprick bubbles.
2. Some sort of chemical spill, including cat/dog pee. There are no drips.
3. Intense heat.
looking at your photo I would say my best guess would be intense heat. Was the clock near a window with direct sun? In the back of a car? Was it near a window with a glass object on the window sill that could act like a prism?
I went to look at a grand piano once that had very similar bubbles on the inside curve of the side, I looked at the window which was about four feet away and hanging in the window was a large diamond like semi precious stone. Your friendly local fireman will tell you how many house fires are started like this.
I notice also from your photo there are a few small bubbles above the main area of damage that have not burst, which to me, points at heat rather than chemical as the polish is lifting from underneath rather than being attacked from above. There also seems to be some damage on the moulding on the front bottom box but this could be the photo!
Hope this helps. If you want to bring the clock case to me to have a look at you are welcome to do so or you can give me a ring any time.
Regards,
Paul.

 

[RogerS]

Hi Paul

You might have hit the nail on the head. It's definitely not (1). Possibly (2)

but it was collected by him yesterday morning in his estate car. Two hour drive...maybe something in that re the heat. Or where he has/had it located at his home.

Many thanks for your kind offer. I'll probably be going up to take a look at it either today or tomorrow.

 

[RogerS]

Oh c**p... :idea:

Well done, Paul. You are bang on the money. It is almost certainly (2). I remember now that there was a thin line of shellac visible where the panel met the moulding and I ran a fine brush down it with spirit stain.....which must have dripped or sprayed down ....

Oh ....b*****ks.

 

[marcros]

Any more clues - what is it, where located (much traffic) and any pets?

I'm assuming it's the pitted finish, rather than the white ring (reflection?), that's in question.

Ah, sorry I was looking on my phone and on the small picture it looked like a white ring on half of a drop leaf table!

 

[RogerS]

Following on, I tried to recreate the problem using spirit stain and dropping it onto a piece of the same wood and finished in the same way. Zero effect...nothing. The beeswax formed a pretty good seal.

Talking with Paul (MrP) he's taken another look at the photos and is convinced that it's heat related and suggested I went outside with a magnifying glass to see if I could recreate the problem. Yes ! The shellac melts (especially if you get the focus just right and heat up the layer(s) closest to the wood. It then expands and delaminates the layers of shellac leaving the top layers unsupported and easily brushed off leaving the craters.

 

[mrpercysnodgrass]

Soon to be seen around the streets of Oxford solving murder mysteries!

 

[Woodfinish Man]

Have to say I think this thread highlights exactly why forums like this exist and are so important. We've never seen anything like that...we have now!

 

[RogerS]

Well, I saw it at first hand today and tbh it doesn't look anywhere near as bad ! But still needed fixing...and so now back in the workshop for that piece of moulding to be stripped down to bare wood and refinished...such is life.

 

[RogerS]

OK...here's my current thoughts. First you can ignore the 'marks' on the small ovolo moulding...that's dried polish where he didn't buff it up enough.



That leaves the main concave moulding. Stripped it back to the bare wood and I noticed a small dimple right where the larger blemish is. Lightly sanding wouldn't get rid of it...seems to be almost like a small fissure in the wood. Now this flame mahogany and so the grain goes every which way and I do know that it can get very very porous and this is where I think the problem came from. It confirms Paul's (MrP's) suggestion that it was heat related...simply that air underneath the finish (in the fissure) expanded in the heat and blew off the shellac. Other parts less 'fissurey' and so only small parts blown off.

 

[Matt@]

Shellac is extremely forgiving. Only time I,ve seen it blister is heat or bleach agent coming through. I put money on heat. If the client parked up with that part of the item exposed for 30mins in hot direct sun theres the answer

 

[rafezetter]

Following on, I tried to recreate the problem using spirit stain and dropping it onto a piece of the same wood and finished in the same way. Zero effect...nothing. The beeswax formed a pretty good seal.

Talking with Paul (MrP) he's taken another look at the photos and is convinced that it's heat related and suggested I went outside with a magnifying glass to see if I could recreate the problem. Yes ! The shellac melts (especially if you get the focus just right and heat up the layer(s) closest to the wood. It then expands and delaminates the layers of shellac leaving the top layers unsupported and easily brushed off leaving the craters.

sounds like another effective "aging" tecnique to me