Is there a way to better check preforms?

[Taogem]

Yesterday was an extreme example. I got to the polishing stage before I realized the cabs were cracked.

I did not see anything wrong with the preforms at all.

Once I began to polish then the cracks showed themselves. 

Short of taking some kind of magnifying glass or maybe a microscope  , would like to know how others inspect their slabs and preforms.

Is there some kind of chemical or process of some kind that I might do that would reveal those hard to see cracks prior to spending the time cabbing?



 

[mirkaba]

You can usually pick out the small  cracks with a loupe. Its also good for checking for scratches....Bob

[Taogem]

It is always agatized material that seems to surprise me. I am not so darn blind that you would think these fractures/cracks would have been seen in both slab and preforms.

I have been trying to be extra careful while polishing. Where I tend to let most cabs get a bit of heat built up during polishing, I do not with agatized marterial. They seem to be extra sensitive and I am thinking that part of my problem is happening while polishing. Even though I have been trying to be extra gentle with the agatized material.

Is using a loop something you do all the time Bob either before cutting out your preforms or even after cutting them out?

Do others here really take as close a look with something like a loop prior to sanding each and every time?

Maybe this is just a dumb question to start with?

I just can't believe that I am missing some of these fractures and having them surprise me when I am wrapping up the cab 

[mirkaba]

I know people that use a loupe all of the time...Habitually....I actually feel  a little paranoid when they whip out a loupe and start  a 5 to 10 minute inspection of my stones. I keep one handy and usually only use it if there are noticeable problems. I do use an opti-visor quite often but not all the time ...Maybe half the time.  Montana agate seems to develop small fractures more often than other agate I cut but that is most always during the grinding stages.  I do try to let my preforms dry for a day or so before heating and dopping, as the expanding moisture can agravate and expand small cracks. And of course there is opal, most often the white or crystal some of which seem to erupt days or weeks after the polishing   This might just be a small, glitchy gremlin like phenomena that you will work through. Good luck   Bob

[freeform]

I habitually dry my cabs before inspecting for new or old problems. I find that you should make sure you inspect your cabs throughly by the 220 stage in sanding. Stones can and do develope fractures, pits, and flaws in general. Or as in picture stones, just simply trying to keep the pattern intact will give you a good run for your sanding skill.

I just wipe them with rags i keep just for this, paper towel can be used but i dont recemend them for this. I always use my thumbs to feel the surface area of the cab for large inperfections, but with fractures or pits. If you know they were not there before triming the preform on your slab saw or grinder. There may be a heat problem, alot of agate is heat sensitive. Allot of jaspers from Oregon and idaho can burn and create blisters when sanding with not enough water, or pushing too hard on narrow egdes.

If you have any examples to point out, maybe we can figure out any insight. I just cut this piece of Willow creek jasper, which had blast fractures in it, but i cut it anyway. These were clearly visable when i cut the slab.

[Taogem]

If you have any examples to point out, maybe we can figure out any insight.

The last few found the wall... :

Here is another from today.

I really took my time. Slow on the sintered wheel, nice and easy with the sanding, and did not let it get warm much while polishing.

I think it just boils down to knowing I have to contribute to the scrap jar on a daily basis 

I did not see any fractures when I started and you can see the two that developed.

[freeform]

Ok, the one in the first and third photo is the same one right? If so, what i am seeing is a flaw. Not a fracture. there is no way around such flaws, the only way is to grind it away. However when working stones with inclusions.(just about all agates and jaspers out there). These flaws can be cut out, if you can see them piror to orenitating your preform. But in the case i see here, it most likly bubble up to the surface when you cut material away.   These types are get priced into my under$10 cabochon catgory, no matter how pretty they may be.

The second photo does look to show a typical fracture, which based on the angle of the cab were the fracture lies, this could of been eaily casued by too much heat, but in my experince when this happens, you see more than one in the area you cooked. Which leads me to believe it was inherinet and there when you started sanding. That could of been caused by your corase shapping wheel, but i dout it looking at the material. I would suspect both were in the stone prior to shapping.   And know that a fracture like the second one, needs to be dryed out in order to properly see. Water will and does travel into that fracture(making it invisiable).

[Taogem]

Yes they are the same, and yes I agree that the one looks to me like it had to have just been within the stone prior to shaping.

The second is really the one I should only have posted. It is really the example of the fractures that appear while polishing. I just can't believe I would have missed it when finishing sanding. Suppose it is possible though.

I don't have a category of cabs discounted based on flaws. I had thought about it, but I just can't imagine why someone would want them for even five bucks.

Maybe I will try a few and see how they do, and if the complaints are minimal.

The nice thing about freeforms is that it really is not a big deal to just continue grinding them down to a slightly different shape in an effort to get rid of these fractures.

More than anything, it is just irritating.

I usually just toss them off to the side until I am in the mood to salvage them.

Thanks Shain..

[freeform]

You hit it right on the nose with freeform cutting concept;

The nice thing about freeforms is that it really is not a big deal to just continue grinding them down to a slightly different shape in an effort to get rid of these fractures.

That how you can get really fun shapes!