"How can I shorten my descriptions and say everything that needs to be said?"
After peeking into a couple of your listings, I found this fabulous ring to have one of your longest descriptions reaching from the top of my computer monitor all the way to the bottom. The first thing I would suggest for your description is to do some grouping of similar information. Keep all the material information together. Same goes for ring sizing and links/shop info that should all go at the end. Once you organize your description, you should be able to consolidate. Maybe you'll notice in this listing that you link back to your shop twice (and have "width and height of this ring" in twice). You should be able to combine information into simpler, easier to follow sentences. The ring sizing information, for example, is hard to follow although a simple concept to understand. A sentence like this may be much better, "This ring is slightly adjustable, but please include your ring size in the Message to Seller for an accurate fit." Straight forward and easily understood conveying just enough information.
There is also some information that isn't serving a purpose for the buyer. Personally, (and keep in mind all of this is a personal opinion), I would not put feedback in your description. That's what your feedback area is for. Think about how much and what kind of information is needed for a potential customer. As a buyer, I don't know what .864 inches looks like. Looking at the image the ring being worn is where I will get my idea of scale. The size of wire is information another jeweler may understand (or find useful to try to recreate the design) but not necessarily the buyer.
I sincerely hope this will help you to decide what information is useful for a buyer and how to organize that information to be more reader friendly. Maybe it will even shorten up the description some.