This guide will address only the ribbons used on the 1897 Zentenarmedaille.  The Prussian 1897 Zentenarmedaille (Centenary Medal) was officially titled the Medaille zur Erinnerung an des Hochseligen Kaisers und Königs Wilhelm I., des Großen, Majestät to honor the 100th Birthday of Kaiser Wilhelm I.  The recipients promptly dubbed it the Apfelorden (The Order of the Apple, due to it's size and color).   Modern German collectors often call it the Zitronorden  (The Order of the Lemon, again due to it's size and color and partly because they forget the name Apfelorden).  Further details on this medal can be found at:  http://reviews.ebay.com/Prussian-1897-Centenary-Medal_W0QQugidZ10000000002369985.

The 1897 Zentenarmedaille original silk ribbon (made in Berlin) is plain yellow (representing gold) which varies in width from 3cm to 3.5cm (depending on the maker).  

• Contemporary Ribbon:  Silk, the weave is 16 rows per cm, each thread is 2 strands of ca. 12 fibers per strand, and it is UV-negative.  Silk, the weave is 17 rows per cm, each thread is 2 strands of ca. 10 fibers per strand, and it is UV-negative.  The vast majority of these ribbons are 3.4cm to 3.5cm in width.
• WWI-era Replacement RibbonSilk, the weave is 15 rows per cm, each thread is 2 strands of ca. 20 fibers per strand, and it is UV-negative.  Silk, the weave is 16 rows per cm, each thread is 2 strands of ca. 15 fibers per strand, and it is UV-negative. 
• WWII-era Replacement Ribbon: Silk, the weave is 15 rows per cm, each thread is 2 strands of ca. 15 fibers per strand, and it is UV-negative.  Cotton, the weave is 14 rows per cm, each thread is 2 strands of ca. 10-12 fibers per strand, and it is UV-negative. 
• Modern-era Replacement Ribbon: Often found in widths of exactly 3.00cm, 3.2cm, 3.4cm, or 3.5cm.  Silk, the weave is 14 rows per cm, each thread is 3 strands of ca. 10 fibers per strand, and it is UV-negative.  Cotton, the weave is 13 rows per cm, each thread is 2 strands of ca. 15 fibers per strand, and it is UV-negative.  Poly, the thread melts and clumps when burned, the weave is 15 rows per cm, each thread is 2 strands of ca. 10 fibers per strand, and it is UV-positive.  Cotton, the weave is 14 rows per cm, and each thread is 3 strands of ca. 8-10 fibers per strand.  Note that some of these ribbons have a false UV-positive due to the use of a fabric finish. Poly-cotton mix, the weave is 14-15 rows per cm, each thread is 2 strands of ca. 10-15 fibers per strand, and it is UV-positive.   

Copies are known and normally sell for almost as much as an original example.  If you are interested in the original or contemporary ribbon, the best advice is:  Buy only from a reputable dealer who specializes in Imperial German medals.  Please visit my blog (http://blogs.ebay.com/tsa-li) and/or guides for further information.  Thank you for your visit!