Slab Sections and Sealing (PCGS, NGC, CACG)

lilolme · September 7, 2025 7:51PM

Taking a break from another project that seems to just grow (due to me), I took some time to do some slab cross-sections and focusing on the point(s) where the sonic sealing should be happening. This was due to seeing a few posts about slabs being sealed or not.

First here is one of many articles on ultrasonic sealing. Do a search and there are many others that might make more sense and some for metal sonic welding. The short of it is - create an ultrasonic sound, transfer to a mechanical vibration, hold parts in tool and apply mechanical vibration to parts to cause local vibration and friction to melt and seal the parts. Most articles are focusing on more simple configurations like two flat surfaces. Below is a 2 minute video showing ultrasonic sealing of a bag (just to get an idea of it).

https://weldingproperty.com/how-does-ultrasonic-sealing-work/

https://www.youtube.com/watch?v=ER-WVi2GM3Q

So I took some of my previous PCGS cross-sections and took new photos with the phone camera since it does close ups better and has more pixels (than the 20+ year old snap-o'matic). Then I got a cheap NGC slab and CACG slab and cut them and sanded the cross-sections to show how they look and/or should function. All three are different to some degree.
FYI - I moved the lights around some and it seemed to mess with the white balance on the phone camera.

PCGS - there is the older slabs (a little purple tint) with a larger notch and tab. The newer slabs, clear plastic, have a smaller tab and the front of the slab overlaps the back. So on both the notch and tab appears to be the focus for the sonic sealing. However, since I have many sometimes see the melting and sealing occurring on the two adjacent side of the front and back pieces.

NGC - first these don't like to be sanded and 'polished'. I remember reading that trying to restore the viewing surface of an NGC is difficult and this seems true for the cross-section. So sections not as clear in photos. The NGC has a large notch in the front piece and then the back piece has a large tab that nests inside the front piece notch. There is a seam about mid-plane around the edge of the slab. Difficult to tell where the primary focus is for the sonic sealing. But does appear to occur between both inner and outer surfaces of the notch and tab.

CACG - I only cut the corner on this one. Plastic appears more like PCGS in that it sanded and polished easily. The front piece is wider than the back and has a frame around the periphery. The back piece nests inside this frame and has a similar frame around it. So the inside of the front piece frame is close to or in contact with the outer frame of the back piece. This might be the primary sonic sealing surface area.

So when asking how well are these slabs sealed, then would need to consider how consistent is the ultrasonic sealing around the entire periphery of each slab. It certainly is going to vary from slab to slab but how much - don't know. Also since each company has a somewhat different design there certainly could be variations there. Things to consider are the fit up, positioning, tolerances of parts and the variance in the ultra-sonic sealing machine / process from slab to slab.

PCGS Photos
This is a sanded cross-section showing a newer slab top and bottom (smaller notch and tab with the front piece extending past the back piece) with an older one in the middle (larger notch and tab and the front piece does not extend past the back piece).
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Full cross-sections with the coin ring included. The older slab (purple tint) is not sanded and is as cracked open.
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NGC Photos
On this corner cut I tapped it until it cracked a little and then separated the left side for ease of seeing the two pieces (at least that is what I was thinking). Notice where the outer mid-plane seam between the front and back piece is.
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These are the slab corner cut and then the opposing sides of a cross-section cut. Again difficult to sand and polish the NGC plastic.
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CACG Photos
Corner cut piece. Then the slab with the cut corner. I did not do a full cross-section cut. It appears sealing is trying to occur between the two outer frames of the front and back pieces.
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coinbuf · September 7, 2025 8:15PM

Interesting.

Mr_Spud · September 8, 2025 3:53AM

Thanks for posting, I find this interesting too.

lilolme · September 8, 2025 10:34AM

Update - I was looking at the CACG slab with a magnifier and said 'that is gapped'. So I inserted some paper between the back piece and front piece on the short side (in this case bottom) and then on the long side at each end.

The first photo shows the paper on the corner cut and down to the base of the front piece (can see in cross-section lines). This goes around the corner and then on the long side for a short distance. This is shown in the second picture. If not sealed between the base of the back piece to the front piece, then would this appear to be an air leak path?

The third picture tries to show where a plastic line stops the gap (red arrow). Is this a sealing line area? Probably should have cut this one across also. The green arrow shows a notch which corresponds to the 9 o/c and 3 o/c position of the round viewing area (notch for space). The last picture is the other end. I was able to repeat this with another CACG slab.

LATE EDIT: Got curious so I ran a box knife around the periphery (all 4 sides) between the back piece and the front piece (example where the paper is but around all 4 sides). Tight fit and could not tell if I was cutting anything. But the slab is still intact or it did not come apart. So on this slab there is definitely some sealing happening between the base of the back piece and the 'shelf' on the front piece.

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Coins3675 · September 9, 2025 10:19AM

Interesting

lilolme · September 10, 2025 2:14PM

Oh no, more curiosity from me. I decided to crack out the CACG slab.
As noted above the base of the back piece rest on the front piece. However, there is a small thin raised outer frame on the inside of the back piece that rest on the front piece. Not sure if that description comes through or not. This thin raised outer frame on the inside of the back piece was 'attached' to the inside of the front piece along its length or periphery. But some of it came apart easily as if it was not firmly attached or maybe not at all.

Below are a couple photos of this showing a clean or unbroken raised outer frame on the inside of the back piece. Then an area where the thin raised outer frame was broken (also included a photo of the front piece in this area showing the broken back piece attached to the inside of the front piece).

Thin raised outer frame on the inside of the back piece looking clean or unbroken.

Thin raised outer frame on the inside of the back piece broken.

Corresponding area on the front piece where the above broken back piece is attached to the front piece.

Namvet69 · September 10, 2025 3:55PM

Very interesting. So is the ultrasonic sealing supposed to make slabs hermetically sealed? Yet toning can be created by gassing under pressure?

lilolme · September 10, 2025 4:44PM

@Namvet69 said:
Very interesting. So is the ultrasonic sealing supposed to make slabs hermetically sealed? Yet toning can be created by gassing under pressure?

So I can only guess a little here from what I have read and looked at. I am not a sonic-sealing pro at all.

The sonic-sealing I ran across (could do more research but I have not) was generally showing flat surface to flat surface as in the video or for tubes.... I did see some auto parts mentioned (headlights I think). So sonic sealing these flat surfaces (and more flexible) would appear easier to do.

On a TPG slab there needs to be an interface, point(s) of contact, between the front piece and the back piece on all four sides of the slab. These are rather hard plastic parts. There would be some tolerances on the parts. Some positioning of the parts and/or fit up. And then the sonic sealing process (similar to the video but obviously going to be different somewhat).

So the sonic sealing would need to melt or fuse the two parts completely and all the way around or all four sides of the slab parts. Sonic sealing or melting/fusing these parts would appear to not be 100% consistent from slab to slab as the rate and location of sonic sealing should vary due to above variables. How much? I don't know but I doubt anyone would want to guarantee consistent 100% sealed. Could be worm holes or areas that just don't completely seal.
Again my guessing at it.

Luxor · September 10, 2025 6:23PM

I was able to open a CACG holder with very little effort using only a razor blade and a jewelers screwdriver.

lilolme · September 10, 2025 7:07PM

@Luxor said:
I was able to open a CACG holder with very little effort using only a razor blade and a jewelers screwdriver.

Thanks, not to surprising although I would have thought the sealing might be more consistent than that. The one I broke open, as shown, I had to break the plastic in places as the sealing joint apparently was stronger than the plastic. Other places it seemed to open more easily.

BStrauss3 · September 11, 2025 6:50AM

@Namvet69 said:
Very interesting. So is the ultrasonic sealing supposed to make slabs hermetically sealed? Yet toning can be created by gassing under pressure?

No, because that would take a 100% melt and probably damage the shell itself.

There once was a short-lived generation of water-tight PCGS slabs, but nobody has made a gas-tight one.

from May 2015:

https://www.facebook.com/PCGSCOINS/videos/10153078623939193/

https://www.facebook.com/share/v/1TLZtS38H2/

Slab Sections and Sealing (PCGS, NGC, CACG)

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