Inclusions & Heating When Cutting Tanzanite

by Steve Moriarty March 30, 2018

Video Transcription

I've run into a bit of an issue here. On this corner here, you can see where that line is ... It appears to run a little deeper than I expected. What I'm gonna do first is ... Seeing as I know I'm gonna have to get rid of this amount of material, at least on this side, I can cut that, and I know I'm not gonna be losing anything. I'm gonna cut there and see what's left of that inclusion when I'm done. It is possible I may have to change the cut style I'm doing. I can see it can be a shield if this is a problem that runs too deep. So, I'm gonna cut a little bit on this facet that has got me out of square a little bit, but I'm gonna cut the matching facet to the other side and see what that inclusion looks like.

This is the part of the stone that's like a facet on the girdle that's got me out of square. That is material I had to deal with, but I can cut on this side and take the equivalent amount of material and see what's left of that inclusion before I proceed. [inaudible 00:22:52]. It does go a little deeper than I thought. I'm not sure if it's above my girdle, but I may miss it. It looks like it could be a problem, so I'm gonna try and analyze this a little more, and I'll get back with you with what I decide to do.

So, this is something that something happens, inclusion that you know are there, but you don't know exactly how deep they run. Looking at this, it runs deeper than I thought, so making this a square cushion is probably not gonna be possible. What I'm gonna do ... I'm gonna cut a little more through this inclusion, try and get most of it out, and then, because I won't be square on the dop now, I'm gonna have to remove this stone and re-dop it to the center. So, it's gonna create a few more problems, because that inclusion I'm trying to miss that's up here is gonna get closer to the culet to the center. It's gonna create a little more problem. This is why I put this stone off for so long, because I knew it was gonna be trouble, but I think we'll get through it. It's just gonna create a little more work.

So, I continue to run into issues with this stone. I've gotten most of the one problem inclusion, and I'm now down to 56 carats. You know, this is where this wintergreen oil comes in handy, because this roughened surface from the cutting lap ... Now when we put the oil on it, you can easily see into the stone through that rough surface. The problem I was cutting out is right here, but ... Can you see it? But if we look further, there's a plane that runs across this direction. I'm not gonna be able to get that completely out. It almost looks like a cleavage plane. Hopefully, it doesn't part there. But, it is vertical. It will be vertical to my table. It will be out the girdle of the stone, so it's probably not gonna show up, as long as it stays in one piece. I'll get most of it out, but there'll be still a little bit of that left.

I also spotted a little crystal in here that ... I hope that's out, because they don't heat. So, this is a disaster waiting to happen, but we hope we'll get through it. I'm gonna re-dop this up. We're now gonna be cutting a cushion that's not square, but still, hopefully, will be a beautiful stone.

Okay, I'm re-dopped once again, and I'm gonna work it, putting the shape in that's gonna, hopefully, remove most of the inclusion that's left. I have a little piece here that, once I put three facets down the sides or five, whichever I decide ... It's gonna remove that. I'm gonna work it, forming a nice girdle and, hopefully, getting rid of most of the inclusions. It will probably be a little bit left of the cleavage plane, but, like I say, it's gonna be right out of the girdle stone, and it's probably not gonna show up.

So, I have finished cutting this tanzanite using the Nubond 325, which is pretty much comparable to a 3,000 metal disk. I'm gonna polish directly from that. To do that, I'm gonna use a BATT lap. The BATT lap is a tin alloy lap that is harder than my tin lap and produces a nice flat facet. [inaudible 00:30:25] the BATT lap, we use WD-40 to clean it off. Then, we get our diamond powder. Get your finger a little greasy, so you pick up some diamond. This is 50,000 diamond, and we spread it across the lap evenly. Now, you're ready to start polishing. I generally run middle speeds on this, anywhere from slow to fairly high speed. I'm gonna start with the ... I've got three rows of step facets at 60 degrees, 51 degrees and 41 degrees. I'm gonna start at the 60 degree, because I've got a little bit of inclusion I want to get out. So, I'm gonna polish until I remove it.

Up to now, while cutting, I used a visor. Visor's much quicker to use than using a loupe, but once you start polishing you're gonna need to move to the loupe, so you can see much closer. I'm making minor adjustments, trying to get back to where I'm polishing the entire facet. This has got just a teeny bit of my imperfection left, so I'm gonna polish a little bit deeper. You don't want to have to polish too far, because you're gonna have to do that to all the other facets. If you have to go too far, you may as well go around and recut rather than try to polish something off. This particular inclusion is very small and it does break the surface, so it shouldn't cause any issues with heat, but better gone than there. That's pretty much got a nice polish on that facet.

[inaudible 00:34:38] polish facet. When I'm talking about the difference between light and dark is when ... That transition between a bright reflection to a dark reflection is where you're gonna see the facet the best. You can see this facet is, hopefully, pretty well polished, not wiped off pretty well, but it does have a good polish on it, smooth, no dots. It's ready to go onto the next facet.

I've finished cutting the pavilion now. I've got three rows of step facets that are at 41, 51, and 60 degrees. Now, we're gonna take it from the machine, and we're gonna transfer it into a V-dop. We're start cutting the crown after the glue dries.

So, it's time to remove our dop from the crown side of the tanzanite. This is where I've had problems before. I didn't dop, put glue underneath the dop, but because of the way it formed to the top of the stone, there will be some glue underneath it, so I will have to heat the dop. This shouldn't be an issue, but, as I've said before, it's been an issue before with a stone that looked much like this.

So, I've got most of the glue picked off of this. You do have to be careful when you're doing this. I want to get as much off as I can. But, when you're popping it out, you can pop a little chips off your stone. So, just be cautious. And then, once most of it's off, I try and go around the edge of the dop quickly and just get as through as much off that as possible. Sometimes, it will pop off, but, I think, in this area, I've got glue underneath it, so we're gonna have to heat the dop. Just put the dop over the flame, hold the stone tightly, putting pressure on the ... Sometimes, it pops off that easily, but try and hold on to the stone. So, we're freed and ready to cut the crown of the stone.

Now that we've freed up the crown side of the stone ... As I told, my cutters, the first thing you have to go after is the problems. This stone has a problem: the angle here is gonna determine what the angle that we're gonna cut the girdle at ... To do that, I usually put it down on the lap, try and get the light in the appropriate position, find out where that's at, and try and visually see what's flat. Not too easy to do. After that, we'll cut a little bit and see just where we're at. This is set at 46 degrees, which is pretty low for the culet angle, but it's what we have to work with.

Still cutting through the glue that was there. [inaudible 00:40:40] set it up a little bit higher, like to get as much height to this first facet as possible, because the lower we cut it, we cut away a lot of the material that's on the rest of the stone. This is the low point that we have to deal with. The rest of the stone ... There's plenty of material. We'd like to keep as much of that as possible by getting this angle up as high as possible. It looks like 55 degrees is about where we're gonna be, which is good. That's a good starting point. So, we'll try to do something like 55, 40, 30, or 35 for the three facets. I'm gonna do a step cut crown. That's formed our girdle, and we are at 55 degrees. I'll finish the step facets around that 55 degrees, and then we'll go on to the next raw facets.

When you start cutting the girdle, you want to take a close look at the facet and try and determine whether it's completely square. As you go around and cut the entire girdle, if this isn't completely rectangular and parallel sides, what's gonna happen is when you get back around to this facet, the girdles are not gonna match. So, try and make it as square as possible, and if it doesn't match up, you go ahead and feather back around and try and get everything to match up correctly.

This is an issue you're gonna run into often, and that's once you get around [inaudible 00:43:45] you get around to where you started and you don't quite match. So, your options are: recut all the facets ... In this case, I don't have a lot of girdle left to [inaudible 00:43:57] ... or you can feather them in, and that means going from this facet to the next facet and just making them closer but not perfect. So, this next facet I would cut until it almost meets at the girdle and then go on to the next one and just feather the end to get them as close as possible.

Normally, this should be at zero. We normally start the lowest facet and set the gauge to zero, but, because we started at the problem and it was on the end, which is actually the highest point, and I used zero there, once I get around to the thinner edge of the stone, my gauge is gonna be under zero. It's not a problem, because we're well above critical angle. When you go to polish, just remember where you started. Remember that, in this case, I was on the end, and I set to zero. So, if you start polishing on the end and set it to zero, everything's gonna work out okay.

I have finished the stone ... not quite as big as I'd hoped for, but inclusions were definitely a problem. I'd hoped for 30 carat, but maybe we're in the 20-carat range.

It's a fairly deep step cut, so I'm hoping tomorrow to take that out of the jar, and we hit at least 20 carat, and I get to still make some money. So, take it out of the machine, put it into a jar of attack, and by tomorrow it should be free. We'll weigh it up and get ready for heating, and then we'll move on to the next half of the stone.

This stone, I've decided to cut it down the blue axis. It's gonna be a deep stone. Some people might not like it, because of the depth, but it needs a lot of help color-wise, as half the crystal didn't have a lot of color. So, I'm gonna cut it right on the blue and hope to get a 10-carat stone. It will be a little overly deep, but we can design a pendant for it ... Christopher Michael design something and build it in such a way you can't see the depth. But, that extra depth is gonna add to the color of the stone, and, because we cut it in a step emerald cut, it should also add to the depth of [inaudible 00:47:26]

21 ... Well, it's time to put our stones in the oven, and tomorrow we'll find out whether it's a bad day or a good day, because ... Here's our stones, we have a 16 carat and a 21 carat. Now, the 21 carat has a little very teeny crystalline inclusion down near the culet of the stone. And crystalline inclusions can be issues. It can cause fracturing. So, what I'm gonna do, I'm gonna heat very slowly, I'm gonna take 24 hours to go up to 1,050 degrees. Hopefully, the slow rate will prevent the expansion of that crystal to create a fracture in the stone.

I'm gonna put them in my vessel and cover them with investment. This is to slow the process of heating. Cover it up and into the oven it goes. This is gonna take about 24 hours to finish this process. Usually, I do it in about 10 hours, but, hopefully, it will be successful and won't have an issue tomorrow. The oven is set and started. It looks like 24 hours and 15 minutes before I can open that oven back up.

We've removed our stones from the oven. They've been in for 24 hours, about twice what I'd normally do, but it's all because of my fear of this stone cracking. It has a few issues inside one of them. As I've noted all the way along this video, I've been a little bit nervous about this particular piece. So, we heated it slow over 24 hours, and it cooled over the last 12 hours. Now, it's time to see what we've got. The risks here are ... The one stone that's included that I'm worried about weighs 21 carats. Even at 400 dollars a carat, we're looking at an 8,000-dollar stone, so that's the risk at the moment.

All right, let's see what we've got. This is the 16-carat emerald cut, lighter color as I expected. Doesn't look like any issues. Kind of a light salon color. Track this down. It looks clean, success! And a really pretty purple color, not the most intense color, but a beautiful stone, good brilliance. What a relief, no cracks. So, we've got a 21 carat that's a little more purple, little deeper color, and a 16 carat emerald cut. So, 37 carats total weight out of our 112 carat tanzanite rough. No cracks and just very attractive stones. So, I would put this at ... Maybe this one 400, 450 a carat; maybe this one somewhere in the 300 a carat price.
Steve Moriarty
Steve Moriarty

Steve Moriarty has been in the jewelry industry for over 30 years. Steve is not only a jeweler, but a gem cutter and designer. He has traveled the world in search of gemstone rough and has owned a retail jewelry store for 20 years located in Crown Point, Indiana.

Leave a comment

Comments will be approved before showing up.

Also in Tanzanite News & Information

Tanzanite vs Amethyst: What is the Difference?
Tanzanite vs Amethyst: What is the Difference?

by Steve Moriarty July 16, 2024

Read More
Mermaid Tanzanite: What is It?
Mermaid Tanzanite: What is It?

by Steve Moriarty October 25, 2023

Read More
D Block Tanzanite: Does it Produce the Best Color?
D Block Tanzanite: Does it Produce the Best Color?

by Steve Moriarty October 24, 2023

Read More