I have had two bottles of GOLDEN Polymer Varnish with UVLS tightly closed on the shelf for five years. Both the gloss and the matte varnishes appear liquid inside the bottles. Are they too old to use?
If they have been stored in adequate conditions, meaning not overly hot or cold over these 5 years, the varnish should be fine. The signs to look for that could indicate problems are:

1. The material when poured looks lumpy, globby, separated or etc.
2. The Matting solids have settled to the bottom of the container.
3. Noticeable chunks of dried varnish or conglomerated matting solids are in the wet material, or dried film.
4. Uneven sheen after the varnish dries.

Many of the above problems can be remedied simply by pouring out the entire contents into a wide mouth container, such as a old smooth-walled drinking glass (one which is not going to be used again for drinking!). Make sure the container will allow you to stir well without spilling over.

Stir the varnish for at least a minute until the varnish feels smooth. Be looking for those dried chunks. After it is well mixed, and seems smooth, you can return it back into the original container. If there was chunks, settling, etc. you probably want to wash the container first.

Next we suggest creating a test painting with alternating dark and light colors, especially white and black, and do some varnishing over them. If the varnish seems to thin and brush out fine, and the dried film looks even with no noticeable solids, you should be fine to use it for artwork. If you do notice the dried chunks, it may still be usable material, but it most likely should be strained first. Pantyhose, fine cheese cloth, and fine mesh screens can be used. Keep in mind we create our products to keep for many years in storage, so we don't anticipate major problems, but we do think it's important to look for these things, especially when the varnish layer is the final application and can be the most noticeable if there are defects.