A while back, I posted about using a UV flashlight to observe hide glue squeeze out when cleaning up joints. The original post is here. I've taken the process a step further, by adding a tiny amount of UV dye to the glue. The results are amazing.
Below is the joint in daylight, without the UV light.
And here is the joint, in daylight, with the UV light on it. I think this is helpful in two ways, not only can it show the location of the residue, but it also highlights the effectiveness of my clean up process! This is especially important on woods that oxidize and change colors, as even hide glue will inhibit the color change where the glue remains.
It also serves to show how difficult it is to keep the glue only in the joints! I was showing off my new flashlight to Andy Jack, when I spotted this.
Looks fine until I turned on the flashlight!
The dye (one ounce is a lifetime supply) can be ordered here. I hated paying the shipping, but I love knowing where all the glue is. To use the dye, I dip the end of a bamboo skewer in the jar and mix my already flowing glue with it. It takes less than a drop to light up a whole pot of glue.