The recent posts by Detwentyate in the Technique and Players forum about trying to find a thumbpick gripping aid and b2rad on this forum about flatpicks. made me think there might be some who might benefit from my own long-ago search for a better flatpick that was easier to grip.
I never liked the picks with holes or twists or thumb loops, and have have always rolled my own flatpicks since, after I had been playing for about two years, I got tired of slippage and the need for a tighter grip to prevent it, which resulted in tired and sore muscles in my right hand. I assume my method might also help those with arthritis. I actually have three methods. Many years ago, after I had been on this forum for a short period, one of the members pointed me to a source (long since dried up I assume) for the old Martin tortoise-colored molded plastic picks with an integral thick grip with a slight concavity and a gunstock-type diamond checkering pattern on the grip. Those picks themselves were lousy, and usually broke after about 1 to 2 hours of playing due to bending fatigue in the brittle plastic, but I used them only for the grips, which I cut off and super-glued to a variety of standard picks, which they fit quite well.
Although I still have a big enough supply of the old Martin picks to keep me supplied with grips as long as I will likely play, I began looking for some other, more universally useable method for accomplishing the same thing. The method I found that works best and is very easy to do is to dip the gripping end of the picks in that liquid rubber stuff that is sold in hardware and home supply stores for use on tool handles. Around where I live it comes in red, yellow and black. If you’re really organized (read, “anal”) you could use color coding to quickly identify pick thickness, since the dipping tends to cover up the printing on the pick. This stuff has a couple of positive advantages. You can use it on any pick, so you don’t have to abandon your favorite pick to get some kind of gripping aid. You can dip the grip-end once or many times (letting it dry between dippings) so you can experiment with different thicknesses (it can get very thick if you like). It also tends to get grippier if it is slightly wet. I sometimes lick my thumb and forefinger first to accomplish this, but if your fingers sweat, the effect might be automatic. Another thing is that even without the stickiness of the stuff itself, the taper between the grip end covered with this stuff and the flat, picking end makes its geometry very easy to hold without a death-grip to prevent slipping.
The third method I use is a hybrid combination of the first two. If you don’t have any of the molded Martin picks you won’t be able to do this, but it’s my personal favorite. A glued-on, concave, diamond-checkered grip covered with liquid rubber.
The biggest problem with this method is that the liquid rubber comes in cans big enough to use on about a thousand picks (maybe more), and once you open the can it tends to dry out quickly. I pour the leftover into jars and seal them tightly so it lasts much longer. At least a year or two in my experience.
Since I started using these methods, I have been able to hold flatpicks with a very relaxed grip, even when doing fast and intricate cross-picking. I believe this has improved my playing and learning. You might give it a try. It’s easy and cheap to experiment with.