You asked: "Are your "preserved" products glycerin preserved....especially the greenery/filler items?"

Answer: Many of our preserved foliages are systemically preserved with a solution we developed over ten years ago. One of the ingredients is glycerine. We believe that the other systemically preserved items we carry, that are processed by others, also incorporate glycerin in their formulas. The pressure treated preserved items, which are subsequently painted, probably do not use glycerin, but due to the proprietary nature of the process, we cannot be certain.

Examples of products treated by our process are:
Preserved Ornamental grasses such as Cascade, Buffalo, Bear etc. Preserved Trees such as our Arborvitae Preserved Foliage such as our Oak Leaves. Preserved flowers such as our Caluna (a true Heather) and Sweet Annie

All the above are grown on our farms in Oregon.

We attempt to preserve the above items to look as natural as possible and generally they stand up well to humidity as well as dry conditions without weeping.

Some people preserve leaves by immersing them in glycerine /water mixture for a while (depending upon the leaf).
The glycerine is absorbed through the leaf surface. The leaf is then washed and dried. The glycerine destroys the color of the leaf and it takes on an oily appearance and feel. Some people add a dye to the solution so that for example the leaf is dyed green at the same time it absorbs the glycerine, thus making it look more natural.

The best way to treat leaves is with a glycerine and water mixture by placing the fresh cut stems in the solution and allow the leaves to draw the solution up. This is called systemic preserving.
Systemic preserving has become quite sophisticated as a technology and most manufacturers have developed formulae in which glycerine is a large component, but by no means the only component. Various other additives (our trade secret) are added to overcome problems such as bacterial spoilage, uneven-ness, wheeping, shriveling etc..
So although it might be fun to try the process, your time might be better served by simply leaving it to the experts while you have fun designing and creating your works of art.