Significant performance differences between silver and aluminium reflective layers highlight the importance of knowing what you are buying
The material that is used for the reflective layer of a blank CD or DVD is a critical factor in the failure rate of the disc. The layer reflects the laser beam back to the laser photosensor in the laser head, so if this reflection is not precise and consistent, the disc will incur errors when writing to it or reading data from it.
The reflective layer is most commonly made from aluminium or silver. Discs with aluminium reflective layers are generally cheaper, while silver layers offer superior reflectivity which can provide improvements in read and writing performance. What needs to be understood is the significance of these performance improvements, and whether it justifies the price difference?
Also, in making this assessment, it is necessary to note that lasers in optical drives deteriorate over time and become less powerful. It is therefore relevant to understand how well optical discs perform in drives that are relatively new but also to see how well they perform when used in optical drives that are older.
HIGH FAILURE RATE OF ALUMINIUM
In tests using new optical drives (under 1 year old), the failure rate of burning content onto the aluminium discs was greater than 10% for DVDR and more than 13% for CDR compared to zero failures for silver. However, when used on the older optical drives (over 1 year old), the burning failure rate was notably higher – over 15% for DVDR and over 25% for CDR, again compared to a zero failure rate for silver. In addition, when executing the error rate tests, the silver layer products all performed within the book specifications (DVD: PI sum8<280 and CDR: C1<220) while all of the aluminium discs were out of spec., with significantly higher errors recorded when tested on optical drives over 1 year old.
These performance differences can be attributed directly to the inferior reflectivity of the aluminium layer compared to that of silver.