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 Post subject: Asscher Cut
PostPosted: Sat Jan 23, 2010 9:00 pm 
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Since I have a stone for recutting that fits an asscher design, and thanks to Roger for the angles, I've recreated it in gem cad. Those who would like a .gem file please pm me w/ your email address and i'll forward it. The gemcad file is set for corundum btw.

Here's a link to the pdf file, seems photobucket won't give me thumbnails...

I'm going to test cut this on syn corundum before I put the burmese ruby to the wheel.. I'll post pictures on this once the test cut is completed.

One of the things I noticed in bog analysis is just how bad this design seems to be! I think roger also noted that as well, hence the test cutting i'm doing. We'll see how it turns out, as anything is an improvement over those native angles. Any feedback/advice on the asscher's is welcome here.

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PostPosted: Sun Jan 24, 2010 8:10 am 
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Thanks for the .gem- file John. i played with DiamCalc for a while...

Pic 1. Ruby spectrum is not one of the easiest to render but you can get the idea what is coming up. You can find movie version of it here.

Image

Asscher is all about patterns so i think it's not best idea to BOG-optimize it for brightness. Here you can see two images with same diameter but very different pavilions. I used colorless sapphire to see patterns more clearly.

Pic 2. This is original (7mm 1.96ct), it's good if you have deep native and you want to cut for yield.

Image

Pic 3. This one (7mm 1.70 ct) has very low pavilion and it really suprises me. P5 (35.70 deg) and P8 (31,48 deg) are BELOW critical angle, yet it seems we have very good pattern near the culet.

Image

Pic 4. This pic has grid paper under the low profile stone. You can see it actually is leaking near the culet but you still see lots of table & observer head reflections. Asscher seems to break all the rules! I quess i have to test this with the real stone.

Image

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PostPosted: Sun Jan 24, 2010 12:10 pm 
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Mikko, can you import a GemCad file into Diamcalc? I thought there were just standard cuts available in Diamcalc.

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PostPosted: Sun Jan 24, 2010 1:33 pm 
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Yes you can. Actually .gem is closed file type but you can import .asc- files to DiamCalc and then export it back to .asc -> GemCad.

This is quite expensive software (290 euros) but it's really cool. You can import your cut, then select your gem type (RI, dispersion), spesific gravity and absorption spectrum.

Newest version of DiamCalc has "Advanced Cut edit"- tool. You can see snapshot here. I don't use it much for cut planning but to check actual tier angles.

Normally i just change pavilion or crown depth in DiamCalc until i find best look in certain lightnings. Then i just check some tier's angle from Advanced cut edit and make tangent ratio change in GemCad (no need to import/export multiple times).

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PostPosted: Sun Jan 24, 2010 2:53 pm 
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Hi Mikko,

Do you know if the software can handle dichroism?

Thanks,
Gary

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PostPosted: Sun Jan 24, 2010 2:57 pm 
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Well, aren't I embarrassed :oops: . I thought those were actual cut gems and was going to say how great they look :lol: . Can't wait to see the real thing soon!

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PostPosted: Sun Jan 24, 2010 3:13 pm 
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Hi

Haha me too Morning :oops:
cant wait to see pictures now :wink:


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PostPosted: Sun Jan 24, 2010 5:44 pm 
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Great work mikko! and much better than my bog results.. asschers are really tricky.. I have the pavilion ready for prepolish on my test cut and should have it done by today.. i'll shoot a picture and put it up when I'm done.

Roger reported in a pm that asschers don't work too well unless they are medium toned or lighter.. so the test cutting is important to see..

thanks!

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PostPosted: Sun Jan 24, 2010 9:56 pm 
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ROFL MoDo, thanks for the day's giggle. :lol:

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PostPosted: Mon Jan 25, 2010 3:04 am 
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Gotcha MoDo :smt105

Quote:
Roger reported in a pm that asschers don't work too well unless they are medium toned or lighter


That is very true. That's why i used colorless sapphire to see patterns.

DiamCalc has been developed for diamond indrusty, so there is no pleochroism feature. I have seen these guys doing amazing things and would not be suprised if they can make this too. But then it would be too complicated to use it anyway. You should use two or three different absorption spectras, you should know orientation of crystal lattice etc etc...

You can compare images with different spectras anyway. I have for example spectras for pure red ruby and orangish red ruby.

Yesterday i wanted to make test cut but figured i don't know how to do it :( How do you make sure you make properly sized tiers jleb. I remember somebody has developed meetpoint version but can't find it.

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PostPosted: Mon Jan 25, 2010 3:26 am 
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"How do you make sure you make properly sized tiers jleb. I remember somebody has developed meetpoint version but can't find it."

I'm sure there is a better method but here is how I learned. It works best with just three tiers and also helps if they are equal widths.

Cut the first and last tier until equal size - On jleb's diagram that's 2 and 5.

If this was just three tiers you then cut the middle tier until all three are equal sized.

With four tiers you cut 2 and 5 as above and then cut either 3 until 2 is the width you want or 4 until 5 is the correct width. Then cut the remaining tier.

Adjustments will be required. :)

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PostPosted: Mon Jan 25, 2010 10:10 am 
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Mikko, I had a look at the demo for Diamcalc, and think I will buy the program . I use a Mac with Windows running in Parallels, which didn't allow me to use the full photo render, so I'll have to use BootCamp to run Windows.

Anyway, John, I think you have the cut corners too large on your GemCad file. Typically an Asscher has smaller corners than sides. I find also if you cut the first windmill pavilion facet just below the critical angle it looks nice and stands out well.

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PostPosted: Mon Jan 25, 2010 11:46 am 
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Gene, by full photo render you mean HDR (high dynamic range) ?

I think it is essential. HDR needs new enough video card. Octonus has a free test program at their website to check your card, please find it here. You probably knew this already but i think it's worth to mention in case someone else is interested.

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PostPosted: Mon Jan 25, 2010 8:57 pm 
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Quote:
Yesterday i wanted to make test cut but figured i don't know how to do it :( How do you make sure you make properly sized tiers jleb. I remember somebody has developed meetpoint version but can't find it.


Yes that is a challenge.. plus going back and getting all the tiers lined up! I discovered what Roger and the others were moaning about in having to go back and tweak them.. which i've done...

Gene, check this out blue nile

They run 1.00 on the l/w ratio.

here is a design patent someone got showing what your talking about. I guess they range all over the place..

This page gives some diamond l/w ratios. Looks like the industry is pushing 1.0 l/w ratio

Unfortunately I was over at jeffery's doing some photo work and we plugged the usb port of his computer into my camera. I promptly lost the autofocus capability (looks like something in the chip) so it's off to the shop. I'll get pictures up when the camera comes back.

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PostPosted: Mon Jan 25, 2010 11:46 pm 
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I find that the easiest way to cut an Asscher is to cut all the facets, to prepolish stage, using only a square to start. It's only meet point at the facet junctions of each tier at the corners and you still have to estimate for tier width. The beauty of this is that when you come back to cut the corners in, it is meet point and goes very rapidly from there until it's polished. Trying to cut all the tiers at once on these can be an exercise in futility. Here's a small Asscher in pale blue sapphire, 5 tiers pavilion and 3 tiers crown.

Image

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