As some of you know I am a repair cutter to the local jewellery trade here in Vancouver, Canada. Although I repair for a living, I also know how to damage, and would like to share a short list.

Although a valid enough term for describing many types of fault that all look quite similar, a scratch may not necessarily be a scratch.

For a new faceter any nasty looking line or lines that show up during the polishing procedure that stretch across an otherwise nicely polished facet are scratches, or are they?

I have to point out that this post was not intended to be about any particular person or any particular lapidary equipment and I hope it is received in the general tone intended.  Just to get this argument off to a good start let me begin by saying “the only laps that scratch are called cutting laps”

To begin I have listed the Pseudo scratches, or scratchoids. They look like scratches but aren’t;

Agglomeration;
The polishing medium, lubricant, lap material and swarf combine to form a facet tearing gouge or gouges across a facet. Usually too much of everything is being used.

Aggregation;
The polishing medium clumps and causes similar damage as agglomeration but tends to be less tearing but deeper gouges. Excessive polishing medium is the only cause.

Subsurface damage;
Aggressive roughing laps can cause some material to sustain minute hairline cracks below the cut surface. These cracks do not become visible until the facet is polished. The tracks are seldom straight and do not all go in the lap direction.

Cutting checks;
Failure to sufficiently remove aggressive cutting furrows with a pre-polish leaves remnants that show up when polishing. The tracks will go in the cutting not the polishing direction and not be consistent, usually dotted lines.

Polishing checks:
Failing to sweep a facet or using excessive speed can produce polished furrows that often can only be seen by viewing at certain angles. The tracks are uniform straight lines in the direction of polish

Excessive amounts of polishing medium can also make similar furrows, it can also cause other damage sometimes showing up in Quartz as chevron shaped etchings or waving of the surface.

Burn marks;
Usually only show up on the trailing edges of facets being polished with discoloured tracks that start from mid-facet and get darker towards the end. Can be caused by heat generating laps, excessive speed or lack of lubricant. seldom are they deep.

Heat cracks;
More sensitive stones can suffer from cracking instead of burn marks and instead of discoloured tracks you can find fine hairlines that are random in direction. Very thin Quartz sections are particularly prone to this type of damage.

Low Speed damage;
For any given material, lap, polish medium and facet size there is an optimum speed range that will produce a polished facet. Too slow and it is possible to get random tracks across the surface, hair fine but with no obvious direction. Usually this can be easily fixed with additional speed and/or pressure.

High Speed damage;
Too much speed can cause heat cracks and burn marks but if the stone isn’t being heated it can produce tracks that have no discolouration. Usually on the trailing edge of the facet in the direction of polish and usually only part of the facet. This is caused by the stone ‘hydroplaning’ which allows polishing medium to agglomerate under the facet even when minimal amounts are used.

Low Pressure damage;
Very similar to low speed damage except that too little pressure will take a bit longer to produce similar results. The cure is identical

High Pressure damage;
Too much pressure can also cause rapid heating resulting in heat cracks or burn marks. However, once again if it doesn’t heat up It can produce tearing, usually not very deep and only on the leading edge of the facet. Tracks show as dotted lines deeper and more obvious at the leading edge fading out by mid facet.  Annoyingly it can often be just the one track.

Index error;
On a day when everything is going wrong a missed index can take out 2 facets in one swipe. The usual result of index missing is a lap gouge which can also cause problems later, or an unwanted extra facet. If using a design with close indexing and you have generous amounts of polish, it can cause agglomeration damage on two facets at once. See also ‘adjacent facet’ damage.

Angle error;
Not having the facet completely flat on the polishing lap with some material, particularly Quartz, can be devastating, especially if the trailing edge of the facet is low, Having the leading edge above the lap surface will often allow lap surface material and polishing medium to agglomerate and cause ripping tracks across the stone.

Edge comets;
Many stones can be easily finished with only a cutting lap followed by a polishing lap. A problem that can occur is if the cutting lap was sufficiently aggressive to leave uneven facet edges. Even though a polishing lap is capable of sharpening these edges, polish can collect in the irregularities and show as ‘comet tail’ tracks originating at the facet edges.  Changing lap direction will cure this.

Pit comets;
A similar effect as the edge comets above but originate with a pit in the facet surface. Usually caused as a result of an ‘orange peel’ finish from a previous lap. Also can be caused by surface reaching inclusions. Slow speed and sweeping the stone can usually cure this. Changing lap direction often just reverses the direction of the tail.

Adjacent facet;
This can be quite baffling to newcomers as we see an obviously damaged facet, but it was not the facet we were working on. The tracks are usually facet length in the polishing direction but jagged and dotted in appearance. Invariably this is caused by too much polishing medium but it can be avoided if the sequence in polishing procedure avoids a previously polished facet from being on the leading edge of the facet to be polished. To avoid this type of damage polish facets with the lowest cut angles first i.e. stars on the crown, and chain polish in a direction ensuring that all polished facets are “downwind” from the unpolished ones

Lap medium;
There is no one lap that will polish everything which means there are inappropriate laps which can damage certain materials. Some laps will not show problems until either lubricant or polish are diminished sufficiently for the lap to make direct contact with the stone. Other laps can cause instant damage, for example a ceramic lap is usually a disastrous choice for the softer stones. Tracks are usually jagged and dotted.

Polishing medium;
Just as there is no universal lap there is no single polishing medium. An inappropriate polish usually won’t destroy a facet as rapidly as a wrong lap and more often than not nothing at all will occur. When damage does happen the tracks are usually accompanied by a matt finish on the facet.

Lap too wet;
Although lubricants used on polishing laps are quite varied the most common are water, wax, oil or grease. Water, although certainly easiest, can be the most problematic as too much could result in hydroplaning causing the tracks described in ‘high speed damage’ above. It can also wash of the polishing medium and cause tracks as described in ‘lap medium’.

Lap too dry;
Too little and almost always the stone will quickly heat up, Depending on the material, the damage can be ‘burn marks’ or ‘heat cracks’.  If a lap goes completely dry under a facet the possibility of ‘agglomeration’ damage is very high. Some laps will generate heat very rapidly , Lucite and Plexiglas are among the worst offenders.

Uneven lubricant;
The other lubricants are not at all prone to drying out but need more care to ensure that they perform. An even spread with the correct proportion of polishing medium is more critical to avoid ‘lap medium’ damage but the more usual problem is excessive polishing medium damage, sometimes made worse by using a lubricant and polish combination that is prone to clumping and causing aggregation damage.

Poorly prepared lap;
There are lots of polishing laps available to faceters made from many different materials and they all require a particular technique to perform. In every case however there is a preliminary procedure that should be used to prepare a lap for use,  even if the lap is guaranteed to work perfectly out of the box.

For a lap that comes pre-charged with polish the preparation should be little more than a test with a prepolished piece of low value material that is hand held. Following the lap manufacturers instructions for a first attempt is always a good idea but it may take a few tries to understand the required lubricant amount, lap speed and pressure on the stone needed for it to work efficiently. Achieving a polish in this manner assures later success on more valuable material.

For a lap that requires charging more care is needed to ensure that preparation is according to the manufacturers directions. Particular attention should be paid to lubricant and polish proportions and also ensuring that the entire lap surface is covered before preparing further. Many cutters will use a norbide stick at this point to charge and prepare a lap, the burnishing effect can be advantageous with many lap and polish combination’s. I have always used a synthetic sapphire half boule which does the same job more attractively. The newly charged lap can now be prepared with a test stone as outlined above.

True Scratch

A true scratch can only be caused by some sharp material, harder than the stone being polished, being dragged across the surface of a facet. The appearance is not like any of the tracks mentioned above as it will usually show as a very fine straight line, multiples if it took several revolutions to discover it.

The idea of a contaminant being a single particle or maybe just a few is not as unlikely as it seems. Any more and the occurrence probably wouldn’t have gone unnoticed. There would also be an obvious mark on the polishing lap and the scratch would not be a surprise. There are several ways to introduce contaminants and get scratches;

facet edge failure;
Some gem material will have a tendency to chip along a culet edge when being polished. If the chipped off piece manages to embed itself in the surface of the lap it will produce a scratch. Usually not deep, even if it rolls.

residual swarf;
A lap that has been used for polishing hard materials and then stored without being cleaned may have agglomerated contaminants that aren’t removed with initial lubricants and will scratch a softer material.

dirty fingers;
A  common practice for dispersing polish across a lap is to use a finger. It makes sense to wash ones hands before using polishing equipment.

dirty environment;
Obvious sources of contamination are from a swarf covered splash pan, facet head or drip pan. Less obvious sources are overhead lights, magnifiers and spray bottles.

quill dribbles;
When going from cutting to examining a stone, the quill will be raised and any residual lubricant, swarf and possibly grit may run down the dop stick into the quill. If the stone is then lowered onto a polishing lap the quill can dribble contaminants onto it.

poorly stored laps;
It should be obvious that laps are stored without touching one another and that they should be cleaned after use. Every effort has to be made to ensure that polishing laps don’t come into contact with other laps, so using separate storage or holding devices, one for cutting laps and one for polishing laps and putting them in different places, will certainly help prevent this.

plated laps that shed;
Although plated laps can often provide years of trouble free cutting they can become worn and will shed diamond particles. The problem is that some of these particles will still be bound with the plating metal which prevents them from being easily washed off, eventually one of them will get transferred to a polishing lap.

Finally there is nothing more frustrating than trying to remove a persistent scratch only to discover it’s a surface reaching veil. Sad to admit that after all these years it can still happen. When in doubt magnify, if not convinced, magnify some more.

I would certainly welcome any comments and I am especially interested in any additional methods that have been discovered to interfere with achieving a polished facet.

Tony.