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In page Professional Coin Grading Service:

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The PCGS holder (aka slab) is made of clear, inert plastic and is stackable. Anti-counterfeiting measures include a hologram on the back, markings within the holder, and Near Field Communication (NFC) chip embedded in some holders. [1] Printed on the front of the blue paper insert is the coin's type, denomination, grade, attribution, pedigree (if any), serial number, Universal Product Code (UPC), and other pertinent information.[2][3] First-generation PCGS coin holders are smaller and lack the raised stackable edges of later issues. Their insert was printed on plain white paper. In some of these early holders, the coin will be loose enough to produce noise when the holder is handled, thus their "rattler" nickname.[4][5]