How do we know exactly when a rod should be re-varnished? Well, let's remember that the job of the varnish is to protect the rod & wraps. When the varnish is compromised - to the point that it allows moisture through - it's time to replace it. It's at that point that the bamboo or silk thread of the wraps are coming into direct contact with the outside elements of the world & it won't be long until the glue holding the rod together starts to fail, or the thread begins to fray, if you continue to fish with the rod in that condition.
Let's take a look at new rod varnish. It should be smooth, clear, & have a glass-like appearance to it, like these two rods do:
Keep in mind that by keeping a rod clean & waxed you can greatly prolong the life of the varnish. Wax not only makes the rod look better, it adds an extra layer of protection, & doesn't allow water & dirt to collect on the varnish as easily.
Take a look at the rod varnish below. Here you can see that the varnish is definitely starting to break down. It doesn't have much life left to it. However, if this rod is kept waxed & clean, as well as stored properly out of the sun when not in use, it should be able to make it a couple more seasons before it has to be re-varnished.
I hope this little guide to rod varnish has helped you some. If you have an old rod, or if you're on the fence about buying one that has some varnish issues, hopefully now you have a better idea of how to judge the condition of the varnish. Knowing this can help you to determine if a vintage rod is worth the asking price, or if you need to have an old rod re-varnished before you fish it in order to protect your investment in it.
If you're still not sure about the condition of a rod's varnish, ask a qualified, experienced rod maker that you trust. Showing the rod maker photos of the rod & the varnish in question is always a big help, too. Of course, I'm always more than willing to help out in that department so please feel free to contact me with any questions you might have.