Replies

1. 
   RSRose | Jul 31, 2002 12:00am | #1

   Jayst,

   Any time you finish a piece that has pores visible on the surface and use fine abrasive in your finishing method, some of the abrasive will get trapped in the pores and crevices. It's surprising that it took that long for it to become noticeable.

   French polishing is usually done on the surface of a finish which itself has been applied over a completely "filled" wood surface. There are instructions, for instance, on french polish guitar finishing that spend huge amounts of time on getting the wood surface abraded so that the wood itself acts as its own filler.

   While it is certainly possible to french polish the surface of a finish that has crevices and pores showing, it is inevitable that abrasive is going to remain in the cracks. It is very difficult, if not impossible to get it all out, especially if it is trapped or glued in with shellac. It is hard enough to remove it when it has gotten there as a result of a slurry containing nothing but abrasive and lubricant. You could try using a solvent as lubricant that does not attack shellac (mineral spirits or naphtha) and a soft brush.

   Rich

2. 
   HowardAcheson | Jul 31, 2002 12:45am | #2

   I'm afraid Rich is right, Jay. French polishing is done on a surface that has had its pores filled and is perfectly flat.

   Short of completely stripping the surface, I don't know of a way to get the "white" out.

1. 
   JayS | Jul 31, 2002 01:38am | #3

   Of course, French polishing intentionally uses pumice dust and shellac to fill the pores.  Pumice is not used only as an abrasive to polish the surface.   There is no other filler used, such as por-o-pac (silica).  The pumice dust is essentially microscopic particles of glass, and just as when a piece of broken glass is immersed in a glass of water, it becomes invisible.  So, when the particles of pumice are encased in shellac, they instantly turn from white to crystal clear, and leveling the surface.  That is why I am puzzled about the delayed whitening.  Since the pumice is deep in the pores, sanding off wouldn't be an option, especially on the thin veneers.

    Many people  use the term "French Polish"loosely, to mean padding on shellac over a filled surface which has been filled with wood dust or other means.  This is not the traditional meaning of the term, and is not what I did.   Now that I have clarified my method, any additional thoughts?  Thanks very muchfor the advice.

   Jay

1. 
   RSRose | Jul 31, 2002 01:52am | #4

   Some additional thoughts, only guesses.

   The method that you used is, in fact, the guitar finishing method that I referred to. My understanding of the method is that the pumice generates wood particles of a size smaller than the pumice and the slurry eventually fills the pores.

   I can accept that particles of glass immersed in, completely wetted by and encapsulated by shellac will be invisible. But I don't agree that pumice is glass. It's finely ground lava (rock). Is that glass?

   Either the pumice is not pure glass, or it has trapped air around it, or it was encapsulated and is now "de-capsulating" or the shellac is breaking down in those areas.

   Whatever the etiology, I believe that, short of starting over, nothing is going to improve the current finish. However, perhaps letting the area soak in some alcohol or laquer thinner (to let the pumice re-encapsulate), then spot refinishing?

   Rich

   Edited 7/30/2002 7:00:33 PM ET by Rich Rose

3. 
   RLMillard | Jul 31, 2002 03:29pm | #5

   I have only limited experience with French polishing, (I can achieve the same look with modern abrasives, and in less time) but have considerable experience with mahogany crotch veneer. Crotch veneer is many times if not most times, full of thin and thick spots and areas where the grain is quite "loose". No amount of sanding or scraping could remove these loose areas, and they are difficult to fill with the pumice, due to their size.In my work, since I hammer veneer nearly everthing, the hide glue does a fairly good job of filling the grain, which helps to eliminate more of the large pores. Brick dust was a common substitute for pumice when working with mahogany, in the early history of French polishing, but today earth pigments would be a more realistic approach. I believe your problem may be due to the oil evaporating or penetrating into the wood, which as caused the pumice to reflect light. I always apply a thin wash coat of shellac, to prevent the over penetration of oil into the surface, but the oil is an important part of the process, both for application and depth of grain, so it can’t be eliminated. If you are after the best clarity, then I would (in the future) apply several heavy coats of shellac and allow those to dry for 2 or more weeks, sand back leaving the shellac in the deep pores, and follow with the French polish, using a combination of earth pigments and pumice (this is basically what commercial grain filler is). Or you can carefully mix for color, standard grain filler and apply it to the wood (this is what I do). I have no idea if what I’m about to say will work, but it is what I’d do if I were in your situation. Using a very fine needle, poke the finish where the pores have turned white and apply very thin shellac. This may wet the pumice enough to hide the problem.

1. 
   Biscardi | Aug 01, 2002 04:35am | #6

   Some mixed advice above - some of which is incorrect.

   See if you can find the FWW article by someone named Franks from about 1996 about French Polish.

   You  don't have to fill the surface before FP. If you start with pumice you  will create a slurry of Shellac, pumice and wood dust which will fill the pores. You don't have to squeege that horrid stuff  out of a can into the pores. Padding shellac onto a surface is a lovely way to finish a piece, but it isn't French Polish.

   Could it be that you waxed the piece with a blonde wax which is now more noticible? Try wiping it with naptha and recoat with a dark wax made for walnut.

   Moisture and heat can whitten shellac also. A very light touch with a rubber dampened by Ethyl alcohol (denatured) may be a way to fix this.

   Best regards,

   Frank

4. 
   Elcoholic | Aug 02, 2002 06:35pm | #7

   In FWW #75 there's a similar situation with mahogany and filler in the Q&A section.  Dresden (I think) said it was caused by the oil soaking into the wood and then later coming back towards the surface and reacting with the filler in the pores.  He goes on to say that this condition is peculiar to mahogany.  What would cause the oil to return to the surface?  Heat.  I wonder if your piece was moved to a warmer location, maybe in direct sunlight prior to the problem?  Unfortunately he said there's no fix, short of refinishing.  If I recall correctly, he recommended using vinyl sealer and sanding back prior to oiling.

   John O'Connell - JKO Handcrafted Woodworking

   Life is tough.  It's tougher if you're stupid - John Wayne