Make UV Glowing Liquid & Seal LEDs into plumbing fittings

[DrArclight]

Decided to write up this how-to after the interest in my glow tube thread.

First off, how to make liquid that glows under a blacklight (UV):

This is fairly simple:  Figure out what color you want your liquid to be, then find several highlighters that are that color.  Pull the highlighters apart and drop the ink sponge into a jar.  Pour a bit of rubbing alcohol or plain old water over the ink sponges, put the lid on the jar and shake it up.  I usually take an Xacto knife and slit the plastic wrapper that holds the fiber in the ink sponge before doing this to get more of the ink out.  It's probably best to figure out how much liquid you need and then try to get as many highlighters as you can into that amount of liquid.  The higher the ink content of the liquid, the stronger the glow.

NOTE:  Rubbing alcohol gets a lot more ink out of each cartridge than plain old water, but you need to be sure that your container or fittings won't be dissolved by the alcohol.  The epoxy I used in my original glow tube (explained below) was slightly dissolved by the alcohol, so I'm having to switch my fluid to water only.

In my glow tube (See this thread) the tubing was so narrow that there wasn't enough liquid to produce the glow effect I wanted so I added silica gel to the tube to scatter the light.  I used the larger-grained clear silica gel.  The small-grained stuff packs too densely and blocked too much light.

For sealing LEDs into plumbing fittings: 

In my glow tube I used 1/4" Inside Diameter (ID) tubing and the accompanying brass fittings.  The ID of the brass fittings was just a hair larger than the 5mm blacklight LEDs I was using, so it was easy to center the LED in the fitting.  This same process will work for larger fittings, but you may have to get creative if you want the LED to remain dead center.

What you need for this:

LEDs
Plumbing fittings
small insulated wire to use for LED leads
small diameter heat-shrink tubing
clear epoxy
heat gun or hair dryer
hot glue and hot glue gun (acceptable substitutes: epoxy putty, milliput, clay, caulk, chewing gum, etc.)

Before starting this, make sure you wash your pluming fittings with a mild soap and water solution to remove any oils from their surface.  Warm water works best, and a detergent like Dawn works well for removing oils.  Rinse them when you're done.

Also wouldn't hurt to wipe down the LEDs with the detergent solution, then clean water, then dry them off to remove oil from them.  Not strictly necessary, but better safe than sorry.



First off, make sure your LEDs fit into the fitting you want to use.  for 1/4" ID and larger, 5mm LEDs should work fine, for anything smaller, you'll need 3mm LEDs or figure out another solution.  Once you know your LEDs will fit, solder leads onto your LEDs.  (Remember, the long leg is the positive leg, shorter one is negative.)  Let the solder joints cool, then slide some heat shrink tubing on that fits snugly over the leads and solder joints.  Push the tubing all the way up against the LED.  Use your hair dryer or heat gun (or a match, candle, lighter, etc) to shrink the tubing.

Now, insert the LED into the fitting in the position you want.  For my glow tube I put the LEDs where they were just a hair short of being flush with the end of the fitting.

Now use your hot glue gun, putty or whatever, to seal the end of the fitting where the wires come out.  This is done mostly to hold the LED in position in the fitting and keep the epoxy from making a mess in the next step.

Once your LED is secured in the fitting so it's not going anywhere, find a way to hold it so the LED is pointing strait up.  Use clamps or whatever you have to keep the fitting securely in this position.

Now mix up some epoxy.  Be sure to use the clear stuff.  (JB Weld is grey and will block the light)  I prefer using the slow setting stuff for this rather than the 5-minute kind, particularly if I'm using a metal fitting.  The reasoning is that the rapid-cure epoxies generate a lot of heat while they are curing and can cause the metal to expand slightly, then contract again as it cools down.  This could potentially break the seal we're trying to create.  After thoroughly mixing the epoxy, use a small instrument such as a toothpick to place a drop of the epoxy around the LED in the end of the plumbing fitting.

Now use your hair dryer or heat gun on low setting to gently heat the epoxy.  Heating the epoxy makes it more liquid so it will flow down into the fitting around the LED and it has the extra effect of helping to get all the tiny little bubbles out of the epoxy.  The glue or putty we put in earlier keeps the epoxy from running out the other end.  The epoxy is slightly cloudy right after mixing, but you will see it become clearer and the little bubbles start to raise out of it as the heat makes it more liquid.  Be careful not to overheat the epoxy as it will crystallize and darken and blur the lens effect.

You may have to repeat the application of epoxy then heat several times to get a sufficient amount of epoxy in the fitting.  Ideally you want the LED to look like it's sitting right under the surface of a pool of liquid epoxy in the end of the fitting to get the best seal.  Once you're satisfied that you have enough epoxy in the fitting, it's time to let the epoxy cure.  Go work on another part of your project and come back after the amount of time recommended on the epoxy's instructions.  I usually let my epoxy cure overnight to be sure it is completely cured all the way through.

(NOTE:  Most store brand epoxies cure with a slightly yellowish tint.  It's not noticeable in my glow tube due to the small amount of epoxy and the brass fittings, but if you're using a larger fitting I can see how this might distort the light or be an unwanted effect.  If that is a problem, you can usually get a clear acrylic resin in the silk flower section of your nearest craft store.  This stuff is used to simulate water in flower arrangements and is crystal clear.  It should work just as well as epoxy, though I have not had opportunity to try it as yet.)