Towards the end of last year, I posted a warning about not stacking Blu-ray blanks in sleeves, after being devastated at losing a good number of “fresh” blank TDK BD-R DL discs I paid a good amount for.
It seemed that storing them in sleeves, under pressure, may have caused damage to the coating causing them to fail burning and come out of the burner with a spotty pattern.
Comments included not using PVC sleeves, which is sensible advice since the CD days as PVC outgasses and has a tendency to “stick” to the top foil data layer on CDs and “peels” them off causing permanent destruction. Of course, most sleeves since then aren’t made with PVC.
Albert, a senior moderator at MyCE forums warned:
The sleeves were known to make things go bad after the discs had already been written; good to have confirmation that it can affect things before burning them, too.
The folks who have had issues with storage of previously written discs have been able to revive them with a heat gun to undo the pattern left by the sleeves. I’m not sure if the same revival technique could have helped, or if there was more damage done than just that.
cd pirate, a MyCE resident replied:
I’ve also noticed this myself back in the DVD days.
You don’t need to have anything pressed on top either. Sometimes just the pressure of having two discs back to back in a cd/dvd wallet with the whole wallet filled with discs can cause it.
Some wallets are tighter than others too. I’m currently using a sleeve system but the discs are stored upright with no pressure from other discs so we’ll see if that causes any indentation.
BD-R discs “hard coat” probably gets more messed up than cd/dvd too. It’s probably just a lacquer or something cheap. Would have been nice if the plastic itself was scratch proof.
I never had such issues back in the DVD days myself, so I didn’t pay much attention to it. I had already read back over 90% of my BD-R collection to hard disk because of a lack of trust in the discs, so I only had about 30 discs to do. Unfortunately, I had some important things to do immediately, so I left the discs on a shelf and forgot all about them until just recently.
Finishing the Copy Operation
All of the discs that needed to be copied were about 6-year old burns from my LG GGW-H20L. They were stored in PP sleeves (not PVC) and were mostly stored vertically so as not to have pressure pushing against them by stacking. Most of them were TDK Made-in-Japan discs, with only a few CMCs mixed in.
Starting the copy operation, I got read errors on quite a few discs. Looking at the bottom, the dreaded issue which showed with the blank discs reared its head again.
The pattern is hard to observe, especially with a camera, and can only be seen at the edges of bright direct light. It tends to be a cross-hatch pattern corresponding to the patterning on your sleeve material, which cannot be cleaned off the disc using microfibre cloth, or even with high-purity ethanol.
This seems to affect the discs I had stored in sleeves both vertically and horizontally, generally being worse for discs which had been stored for long periods without removing and rotating.
My hypothesis as to the cause goes as follows:
- The data layer sits much closer to the bottom in a Blu-ray disc, covered by a 0.1mm polycarbonate and hard-coat cover. This is barely the thickness of two sheets of paper, or a sheet of laminator plastic.
- The thin cover layer has some pliability, as most thin pieces of plastic do. You can prove this to yourself by carefully flaking off a portion of the bottom layer and trying to pull on it or push into it – it will stretch and dent.
- The sleeves are made of plastic which may chemically react or degrade over time causing outgassing which condenses on the surface and may react with the hard coat to form more “opaque” spots which affects the readout laser.
- The uneven surface may exacerbate this as the pliability would result in a pattern being “written” into the thin layer, affecting its refractive index (potentially) and the focus of the laser (more likely), resulting in a “pattern” of errors in readout. If the errors are dense enough, data is lost.
I really wanted the data back, so being the desperate person that I was, I decided to follow some advice given by Albert – after all, I didn’t have much more to lose.
Heat Gun Treatment
For the heat gun treatment, I decided to just experiment and see what happens. I used my Tenma SMD Rework station, which has a temperature controlled gun. I set the temperature to 180 degrees Celsius, ensured no concentrating nozzle was installed and set the flow to 75/100.
Before beginning, it’s worthwhile to clean the surface of the disc to remove all contaminants, and then blow using a photographic blower bulb to remove all the remaining dust.
I placed the disc with the data side facing up on my flat wooden desk, and waved the tip of the heat gun about 5cm above the data surface in a circular motion, making sure to move around the disc continually to avoid concentrating the heat too long at one particular spot.
Remember that we want to get the plastic hot enough to become a little more pliable to hopefully restore its shape and state, but we don’t want to expose the data layer to too much heat because that will destroy the data. The heating may have a secondary benefit in evaporating any outgassed contaminants that might otherwise have adhered to the surface.
Generally, you won’t need to use the gun for more than 20 seconds at a time as the substrate will begin to warp very quickly, causing it to “rise” near the centre hub ring. If the substrate sets “deformed”, this can affect readability, so I tend to stow the gun and then immediately put my fingernails on the centre of the hub and push down towards the desk to ensure the disc “sets” relatively flat.
You will notice a slight improvement in the surface condition, but it will not restore the surface to perfect flatness. That is not the aim of the process – the aim is just to restore enough readability to recover the data.
In order to gauge the improvement – I took the scans of six bad discs before the treatment and immediately after the treatment.
After heating, the scan doesn’t look particularly appetizing, but it is readable. I was a little cautious, so I decided to go relatively quick with heating. The improvement is apparent, with a more than halving of the error rate.
This one I gave a little more heat because of the bad state of the before scan. Unfortunately, it seems that the outer edge didn’t respond so well to the treatment, and retained its high rate of error. This may have been because of the original burn, thus giving us a clear reason as to aim for better burns as that increases the margin available for degradation. The first half of the disc after treatment is barely even passable for a fresh burn after 6 years.
This disc was not as bad as the others in the middle, but the edge seemed to have issues yet again. Despite the horrid scan, it was possible to read back all the data, although not at full speed.
This one seems like another particularly bad disc, even after heating it with the gun, but it restored it all to under 80 BIS which seems to be the safe threshold for readability in my experience. The reduction in error rate is pretty dramatic however.
Again, improvements towards the edge seem more limited, suggestive of disc degradation, dirt or other influences such as warpage which may affect readability. I did apply additional heat for this round to try and see whether this could be improved upon over the previous samples where I presumed the outside may not be getting enough heat, but it didn’t seem to make any difference. On the upside, the disc did not bubble, smoulder or get damaged despite the rougher treatment.
Another outcome, pretty similar to Disc 5. This makes six out of six heat gun successes – all discs did not read correctly and had CRC errors prior to the heat gun treatment, and all of them were read successfully afterwards.
This shows the value of optical disc scanning. Even if you can’t relate the readouts of the test to industrial test equipment, it still provides a relative gauge of how easy or hard a disc is to read using a particular drive assembly. With digital error correction, a “cleanly” viewed signal after error correction could be moments away from failure. This is the same reason why you have signal quality bars on your digital TV receiver, and noise margin stats on your ADSL modem.
While the discs were read and recovered successfully, they did not exhibit the same readability margins expected of good fresh burns or even degraded properly-stored burns. As a result, these “recovered” discs should be considered expired and due to be disposed, and this is just a last ditch effort to recover the data.
However, it also lends support to my observation that the test thresholds we use are too stringent – in all cases, the after scan was readable on the LG GGW-H20L with no data errors, so if your BIS peaks are below about 80, your disc is quite likely to be readable. Generally, after fresh burns, we demand BIS peaks around 9 maximum, which is very stringent. It didn’t seem repeated treatments provided much benefits – a single round of treatment was sufficient.
In all cases, the heat gun treatment, used judiciously, did not cause any harm and instead improved read error rates. However, I do not take responsibility for anything you do with this information – if you melt your precious disc, or set your house on fire, too bad!
Whatever you do, do not store any type of Blu-ray disc in any form of plastic sleeve – be it written, unwritten, pressed, rewritable. It seems that the sleeves will cause damage to the thinner and more fragile surface of the disc which will cause potentially irreversible data loss. If it’s too late, a heat gun treatment seems to allow for recovery of the data, but does not restore the disc to perfection. Consider yourselves warned.
As a result, I have officially abandoned all use of Blu-ray media for archival purposes. It is not stable enough, or reliable enough depending on the storage method. It’s also not fast enough, and too expensive compared to the cost of hard drive archival. It seems the heyday of optical media is well behind us.