Frederick M. Hueston, PhD  

Stone Care Consultant 

An article by Fred Hueston ran last month explaining the techniques involved in usesing various methods to achive a factory polish.

Powder Polishing–What Really Happens?

For those of you who are interested in what really happens during the polishing process, the following is a brief explanation:

The polishing process has been studied in depth by several researchers. A scientist by the name of Beilby, studied polishing in 1921 and discovered that a stone surface before it is polished contains rough, viable irregularities. Once the surface is polished, these irregularities become invisible. Mr. Bielby postulated that what happens is, the top layer becomes glassy, losing its crystalline properties and has flowed over the surface, filling in these irregularities.  In other words, the polishing powder tears off the surface of the calcium carbonate atoms, and, for an instant, melts as its smoothed over by surface tension. This surface layer that is formed is called the “Beilby Layer.”

It was also discovered that the relative melting point of the polishing powder and the stone influenced this flow. If the powder has a higher melting point than the stone, it will produce a polish. If the powder has a lower melting point than the stone, it will not polish.

Are we confused yet? If you’re interested in the complete study, it can be found in the Royal Society of London, Proceedings, Series A, Vol. 160 (1937). The paper’s title is: Physical Properties of Surfaces IV-Polishing, Surface Flow and the Formation of the Beilby Layer by F.P. Bowden and T.P. Hughes.

How to Polish Difficult Marbles

Now that you have a basic understanding on how marble polishes and how the different processes work, it is fairly easy to figure out why certain marbles won’t polish easily.

Here are some of the reasons:

  1. The marble contains too little, or some cases, too much calcium for the oxalic acid to react. In the case of a high calcium content, the stone may orange peel. An example of a stone that doesn’t react well to marble polishing compound is Green Marble. This is due to the fact that they are mainly a mineral known as serpentine.
  2. Many marbles are really limestone. This is a common mistake that many people make. Stone such as Travertine, Negro Marquina, Creama Marfil, and many others are limestone and not marble. Many limestones have a double calcium carbonate or a dolomite. Which means Oxalic acid will not react like it would in true marble.
  3. Soft spots or what are called mud veins, contain different mineral than the rest of the stone and can result in dull spots. Because theses dull spots are soft, the abrasive in the polishing powder can erode them. This is common in Botticinos.
  4. Technique is one of the major reasons craftsman have trouble with polishing. Too much or too little water or powder can cause the stone to not react, producing a dull appearance.

So, how do you determine which technique to use to achieve that factory polish?

The best way is to experiment and test your techniques. The following are some helpful hints to when you get into trouble.

Tip #1- Try a wet to dry polish. Many marbles do not like a wet polish and will require a dry polish. Start out as you normally would with a wet slurry. Use a hogs hair pad and continue to polish the slurry until it is entirely dry.

Tip #2- Try a different powder. Remember that most marble polishing powders contain aluminum oxide and oxalic acid. Try using a powder that contains Tin Oxide instead. Tin Oxide can be found in a lot of granite polishing powders.

Tip #3- Try adding some additional Oxalic acid to your polishing powder. Some marble reacts well to high concentrations of Oxalic Acid while others many cause orange peel. Experiment with more or less Oxalic acid.

Tip #4- Try Diamond polishing. Some marbles will achieve a factory finish at high grits. I have seen some marbles achieve a great shine at 1,800 grit or above.

Tip #5- Try burnishing. Burnishing is done at high speeds up to 3,500 rpms. You will need to use special polishing or maintenance pads. Do not use standard diamonds since you burn them up. Some name brands are Monkey Pads, Cheetah Pads, Norton, etc.

In conclusion, don’t be afraid to experiment. The worst that can happen is you may have to rehone the stone and start over again. Also, be sure the stone you are working on will take a high shine. Remember, certain marble will not have a deep mirror finish.

Fred Hueston has written over 33 books on stone and tile installations, fabrication and restoration and also serves as an expert for many legal cases across the world. You can send any email comments to him at .