RINGS arranged by most recent to earliest worn from its FIRST appearance starting Engagement Day.
DIAMOND ETERNITY BAND
Feb 11, 2014 The Portrait Gala: http://www.zimbio.com/photos/Kate+Middleton/Arrivals+Portrait+Gala+London+Part+2/9_EfspfKcvo
Feb 14, 2014 The ICAP Art Room Opening: http://www.zimbio.com/photos/Kate+Middleton/Duchess+Cambridge+Attends+ICAP+Art+Room+Opening/QGA1canCkku
DOUBLE FLOWER CLUSTER RING
This double flower cluster ring seems to be a match to her diamond flower earrings and bracelet. The central stones appear to have a yellow hue to them.
Oct 23, 2013 100 Women in Hedge Funds Gala: http://www.popsugar.com/Kate-Middleton-100-Women-Hedge-Fund-Gala-32255359#photo-32258060
Matching bracelet and earrings pictured below.
GARNET AND PEARL BAND
This band set with alternating garnets (3 stones) and seed pearls (2) was first seen on Kate as far back as 2005 and worn several times throughout the couples' dating years. From the time of her engagement and wedding, she has only worn her engagement and wedding rings. This is the first ring she has re-worn from her dating period with Prince William. Garnet is Kate's birthstone and pearl is William's birthstone.
Feb 19, 2013 Duchess visits Hope House: http://www.zimbio.com/photos/Kate+Middleton/Kate+Middleton+Visits+Action+Addiction+6/GcG-40-Q-J5
The pictures below are from an eBay auction and looks remarkably similar to Kate's ring. It is described as a Victorian ring made in 1876 and made of 15K rose gold with garnets and seed pearls.
Credit for this goes to My small obsessions facebook page: https://www.facebook.com/photo.php?fbid=429439103811627&set=a.158912377530969.42450.132426196846254&type=2
GOLD WEDDING BAND
Made in 18K yellow gold. It was made from Welsh gold already owned by the Royal Family. You can read more information here: http://www.dailymail.co.uk/femail/article-1372078/Royal-wedding-Palace-confirms-Prince-William-wont-wear-ring-marries-Kate-Middleton.html
DIAMOND SAPPHIRE ENGAGEMENT RING
Prince William presented his mother's engagement ring to Miss Catherine Middleton when he proposed to her October 2010 in Kenya. Their engagement became official on November 16, 2010.
This ring has a large oval sapphire surrounded by 14 round diamonds set in 18K white gold. The oval sapphire is NOT 18 carats in size as reported after Kate Middleton received this ring. It is set in 18K white gold which has been misinterpreted as an 18 carat oval sapphire. A possible carat size (12 carats) and brief history on how Diana selected this ring can be read here: http://www.dailymail.co.uk/femail/article-1330366/Prince-Williams-engagement-ring-Kate-Middleton-sapphire-diamonds.html
More likely, the oval sapphire is at most 8-9 carats. Based on the size of the sapphire compared to Diana's iris (the blue part of her eye which is approximately 12mm), the oval sapphire is about 13mm x 9mm and the round diamonds close to 3mm in diameter.