French Polish Quandry

[carheir]

While doing some restoration french polishing, I noticed something with my pads that I am at a loss to figure out.  I am using 100% linen cloth with cheese cloth as the inner core.  When I start out, it looks and works fine but if I stop and put the rubber in a plastic bag and come back to it later, it has little black spots all over the cloth and the cheese cloth.  I thought the shellac might have some residue in it but I strained the solution and it still happens.  I am going to try and attach a picture I took so you can see what I am seeing.  Any help identifying this condition will be appreciated. 

https://lh3.googleusercontent.com/-p1wkUq6utV8/Th5LmEdwL1I/AAAAAAAACK4/vw-KnigR-kM/s800/IMAG0156.jpg

It kinda looks like mold of some sort because what you see in the picture is minor to what I have seen??

[millcrek]

What are you using for shellac?
What are you using for thinner?
How long is it staying in the bag?

[carheir]

What are you using for shellac?  Siam seedlac, garnet shellac  Happens with both.
What are you using for thinner? Denatured alcahol
How long is it staying in the bag?  Spots will appear during a session regardless of bagging it. 

[millcrek]

If it happen with both the seed lac and the garnet shellac without being bagged, I would suspect your linen. Was it washed? if not try washing it, the polishing cloth sold by Mohawk is prewashed. If it's not that I have no clue. Good luck maybe someone else has an idea.

[R Bohn]

     Just a few more questions.
   Are you polishing new wood or repairing old finish?
  Did you use a steel wool or a steel brush?
  Do the spots in the rag dissolve when alcohol is added?
  Randy

[carheir]

     Just a few more questions.
   Are you polishing new wood or repairing old finish?
  Did you use a steel wool or a steel brush?
  Do the spots in the rag dissolve when alcohol is added?
  Randy

Randy,
Wood age doesn't matter, happens on both.  No steel wool used.  Haven't tried to soak the rag in alcohol to see if they dissapear.  What is your thought there?

[carheir]

If it happen with both the seed lac and the garnet shellac without being bagged, I would suspect your linen. Was it washed? if not try washing it, the polishing cloth sold by Mohawk is prewashed. If it's not that I have no clue. Good luck maybe someone else has an idea.

This condition occurs regardless of what material I use.  I can use an old t shirt and it will show up.  I'm leaning towards something in the shellac is reacting with the mineral oil and causing the spots.  I am going to experiment some more to see if it is the shellac or a combo of the shellac and mineral oil.

Thanks for your thoughts.

[R Bohn]

I have had this happen a couple different ways.
  First I thought you were picking-up wax or contaminants from repairing an old finish
   If you are not repairing a finish, and not enough time for mold to grow, and no steel filings,then I think as the rag is drying or as you are polishing , the shellac is building in the rag.That's why I asked what happens when alcohol is added. I'm thinking the spots will dissolve.
 I don't think its the cloth or oil you are using. Although steel wool will do the same thing and some mineral oil is like mold food.
    Just curious, Not that I think it's part of the problem but, what kind of oil do you use?     Randy

[CBWW]

Happens to me all the time.  I rarely use oil on the pad.  Mix my own shellac from flakes and pad with recyled hospital sheets essentially old cotton rags bought in 25 lbs boxes.  The alcohol is from a local finish supply company that I buy in 5 gal. containers.  I always thought it was just mold but wondered how it would grow with the alcohol in there.  I usually store my pads in an old salsa/pickel type jar.  Who knows how clean it is..... I never put much thought into it till I read this post..

www.cherrybrookwoodworks.com 

[Parser]

I bought shiny new paint cans to replace my collection of glass jars for the mixing and storage of my shellac (which I purchase from our loyal sponsor.)  About six weeks later, I went to use the garnet.  It had turned a muddy brown and the inside surface of the can was tarnished black.  Ditto the orange.  The super blonde and platina were fine.
By happenstance, that afternoon I read an article about corrosion in pipes used to carry ethanol fuel.  Pipes used to transport oil more quickly developed cracks when ethanol was introduced to the mix.  The explanation was that a type of bacteria ingests ethanol and discharges acid.
My experience suggests that they thrive in the darker shellacs, so when you mentioned garnet I thought of this.  Considering how rapidly the spots appear, you might look for a culprit that is reacting quickly with an acid, rather one that is slowly feeding a mold.  Maybe you could use vinegar to test materials.  I am guessing that the cans used commercially for use with ethanol are coated with plastic to avoid this problem.
I returned to glass, this time those heavy jars with flip tops used for preserving food.  Jars with screw tops too often seal themselves shut with dried shellac.

[Antiquity]

Never store mixed shellac in an iron metal container.  The iron will react with the shellac and turn it a darker/black color.  When my father was a wood patternmaker they used shellac brushes with the furrel (sp?) made of leather because the metal furrel would react with the shellac.

I use an aluminum pot which will not turn the shellac dark/black.  This pot is made just for this purpose.  It has a slip on cover.  You can buy it at
http://www.freemansupply.com/AluminumPaintPot2Q.htm.

Dennis Bork
Antiquity Period Designs, Ltd.