Cutting Sapphires - "Simple Heart"
by Jeff Graham, Old Pueblo Lapidary Club
I have a lot of people tell me that they have trouble cutting Sapphires, so here is an article about how I do them. I am going to be cutting a new heart design of mine called "Simple Heart".
I am going to use a piece of man-made Ruby corundum to cut this design. This type of material is easy to buy almost anywhere. I though a heart for Valentines day should be red...
The Simple Heart at left is 11.8mm x 11.1mm x 7.4mm deep cut by Jeff R. Graham
This is a piece of man-made Ruby that I sliced off of a corundum boule. I am starting with a piece slightly rectangular in shape.
Notice that I used a rough lap (100 grit) to cut a flat onto the split side (of the boule) of my piece of Sapphire. This makes dopping a lot easier and because the boules are almost polished where they have been split, it was necessary to do this to get a good wax joint. The wax works better on a rough surface. I clean the surface well with alcohol, before applying my lacquer solution, (before dopping).
Sapphire is dopped... If your machine is keyed, be careful and align the points of the stone to the shape of the heart design so that you will not waste rough.
Lap: I am using a 100 extra grit (it has more diamonds than a regular 100 grit lap) to rough in this stone... This is a fairly large piece of man-made Sapphire and I want to get it done. If this was a smaller natural Sapphire, I would probably use a well worn 260 grit lap for roughing it in. Which is still a pretty coarse lap, especially for a smaller stone.
Note: That I am cutting to a good center point, even using what most people would call a very coarse lap. This is a very good habit to get into... Always use a lap that is coarse enough to get the job done fairly fast, but be sure that you are cutting accurately. Meet your center points and other meets, do not over cut the facets . Over cutting will cost you a lot of time and trouble later. When selecting a lap "don't send a boy to do a mans job..." use a lap that is coarse enough to get the job done fast. Use a light touch so you do not over cut your facets, this will make your laps last a lot longer and cutting stones much more enjoyable. There is nothing worse than spending an hour to roughing in a stone, when you should do it in 5 minutes with a coarser lap..
P1 & P2 facets are cut to center point.
Important: Be sure and cut P1 and P2 to center point over the center of the dop. Because this heart (almost all hearts) is 1- symmetry, it is possible to cut to center point and not be centered on the dop. P1 and P2 are opposites for easier centering during the initial cutting. The top of the heart is 12 o'clock in all of the pictures.
P3, P4, P5 and P6 facets are cut to center point.
P7(G) Cut to meet P1 point.
Be sure and cut the girdle facets as evenly as you can, when you cut them to meet the pavilion tiers. A mistake, especially over cutting here can cost you a lot of time and wasted rough. Tip: I use the coarse lap to get close to where I think the final girdle line needs to be, but leave the girdle just a little shallow. I cut it to the proper depeth on a finer lap.
P8(G) to P12(G) are cut to meet their respective pavilion tiers forming the heart out line.
P1 & P3 Cut to meet point with a 600 grit lap.
On a small natural Sapphire I would usually go from a worn 260 grit lap to a worn 1200 steel lap. Because this is a large piece of man-made Ruby I am going to a 600 grit steel lap from the 100 extra grit lap. I need a lap that will cut faster, so it does not take too long.
Above and at left, all of the pavilion facets and then the girdle facets are cut to meet with a 600 grit lap. In the picture on the left I have used a 1200 grit steel lap to fine cut all of the facets before polishing. Notice that I have cut in P13 with the 1200 fine lap...
Here is where a most people start to have problems...
Sapphires Typically will be slightly harder in different directions (on different facets) and also some facets will pit on a fine lap.
This is normal...
In the picture above you can see that one of the girdle facets is definitely pitting. On man-made Sapphire these traits do not tend to be as severe, but they are present.
The pits typically show up on a fine lap, you usually will not see them on a 600 grit or lower.
Some people try to just cut to a 600 grit lap and polish from there (a 600 Nu Bond will pit usually).
I personally do not feel that that is the right thing to do... I think that the pitting is part of the crystal structure and they (the pits) are going to be there, whether you cut to a 600 grit or to a 1200 grit pre-polish (that has been my experience). I think that you will still need to polish through the pits either way. That being said, it is a lot easier and faster to get a good polish from a 1200 pre-polish. If you try to polish from a 600 grit pre-polish, you will be polishing for a long time. If you want to do it from a 600, feel free... I usually leave the facets that are pitting just a little bit short of meet point. So that when I polish the pits out, I do not over cut that facet.
I polish all of my Sapphires using an 8,000 diamond and then a 50,000 diamond polish on Zinc laps. I find that this is the best combination for me. I should point out that I cut very little man-made material, which tends to be cut into larger stones than most natural Sapphires that are available. If I was going to cut a lot of larger, man-made Sapphires, I might consider adding a 3,000 diamond/Zinc lap.
Above: The middle (shiny) girdle facet was pitted, as you can see the 8,000 pre-polish with a Zinc lap got the pits with no problems... It was quite fast too.
I usually run my Zinc laps pretty fast (3/4 to full speed) when I am polishing Sapphire (Chrysoberyl too). If the lap(s) slow down, I give it a good shot of diamonds (I use the Crystalite pump bottles). I am not shy about using more diamonds with Sapphires and Zinc laps. I have never had any scratching problems with these lap.
Above Left: The pavilion and girdle are polished to 50,000. Above Right: The stone has been transferred.
Careful: It is very important that you clean the pavilion and girdle very well (I use alcohol) to get rid of any oil/lube that is left over from polishing. Otherwise the wax will not stick when you transfer.
C1 through C6 are cut to meet girdle with a 600 grit lap.
I would generally use a 600 grit steel lap on this stage of cutting no matter what type of material I am cutting. A 600 is fast, but fine enough to get the cheat set (if needed) and the facets lined up with the girdle.
I line up and cut the crown... Then cut the girdle to the proper thickness, maybe just a hair thicker than I think I am going to want it when the stone is finished.
The next thing that I do is... I cut all of the crown break facets with my 1200 steel lap. I do this for several reasons. One is that the cheat, especially on a larger stone, often needs just a nudge to line everything up when you cut the breaks with a fine lap. Another is that I tend to cut all of the rest of the facets to meet point with a 1200 lap because it is finer and even though it cuts a little slower... It is better to go a little slower here than cut though a meet and have to re-cut the entire crown again.
Above and at left... C7, C8, C9 are cut to meet girdle using a 1200 grit lap.
Below left and right... C10 is cut in to meet girdle, and C11 is cut to meet C6.
At this point, you need to look carefully and see if all of your meet points are correct. Also look for any facets that seem to be pitting or not like the others... Cut them a little short of the meet point(s), if you find any.
At left: This is what the crown looks like with all of the facets cut in, if yours looks different, then you may have a problem...
Notice the facets all look the same on this stone, no pitting (yet)...
At this point on most other types of stones I would go ahead and start polishing the crown. I would polish from the crown breaks in towards the table, leaving it for last...
But this is Sapphire...
With the typical pitting and hardness going in different directions in Sapphire, I am always careful to cut the table at this point. Why? Well what do you think the odds are that the pitting will show up on the table? About 100% if you assume it will not... On this stone I had a good hint, there was no pitting anywhere else on the crown... So guess what???
Well the odds were 100% that I would have pitting on the table when I cut it in.
This stone finished out to be 11.8mm x 11.1 mm x 7.4mm deep
Even though this stone is pretty large and the table is correspondingly large, the pits are really not a problem. The key is to know ahead of time that it is pitting and cut the meets a little short.
If I had polished the crown and then cut in the table, it would have been much more difficult to get all of the meet points on the table to meet correctly.
Polishing the Table...
Above: This is what the table looks like after I have polished it with my 8,000 Zinc lap. As you can see the pits were no problem and the table actually only took a couple of minutes to polish...
At this point all that I had left to do was polish the table with 50,000 and Zinc (while I still had the same setting).
Next: I started out on the crown breaks and polished them all in with my 8,000 Zinc. When that was done I went back and polished all of them with my 50,000 Zinc diamond lap. The 50,000 really make the facets "pop".
Some people only polish to 14,000 diamond when they cut Sapphires. This is actually pretty standard in commercially cut Sapphires, but I think that the 50,000 polish is really much better, and recommend that people use it...
Man-made Sapphires are really not too bad to cut once you have done a couple and learned how to deal with their idiosyncrasies. Man-made Sapphire is easier to cut than most natural Sapphires that I have ever cut. Man-made Sapphires seems to be generally more docile, I suspect because they are not subjected to the extremes of nature while forming.
Also man-made Sapphire is pretty much a breeze to orientate, there are some man-made colors that do need to be orientated. Some colors (blue and orange are a couple) tend to have their strongest color zones out near the rind of the man-made boules. You will need to put the pavilion down into the color zone on these boules.
But other than that, man-made Sapphire is inexpensive and predictable to cut. I recommend that people cut some man-made Sapphire before trying more expensive natural Sapphire rough.
Natural Sapphires, besides being a lot more expensive (assuming you can even find some decent rough) can be much more difficult to cut. Orientating natural Sapphire often takes an expert, and cutting them is usually unpredictable. But after cutting some man-made Sapphires, I recommend that people cut some natural material. Sapphires make beautiful and unusual stones, not to mention valuable.