Several commercial luminescent marker products are available. Off-the-shelf solutions (such as those from Luminlay) are available in several sizes or raw sheet, costing upward of USD$20-30 plus shipping for enough to do a full instrument. A more temporary solution exists in the form of pre-made stickers that fit over existing inlays or sheets of adhesive-backed vinyl that can be cut to whatever shape you please.
For relatively little expense, it is laughably easy to make several sets of your own high intensity luminescent inlays, even making sizes and shapes not commercially available. Casting our own dots and some simple side line markers using materials that are a cinch to get ahold of produces a high quality alternative to ready-made dots.
You will need:
- Luminescent powder
- Good quality two-part epoxy or casting resin
- HDPE sheet such as a kitchen chopping board
- Drill bits corresponding to the size of dot to be made
- Masking tape
Most importantly we need luminescent (glow in the dark) powder. This is easily available from plenty of sites around the net, eBay and Amazon, etc. Strontium Aluminate (SrAl2O4) powders are the brightest and glow for the longest time, but can only produce a limited range of colours. More "difficult" colours such as red tend to be Yttrium Oxide Sulphide or Zinc Sulphide. These have lower brightnesses and glow times than Strontium Aluminate. Powders are often available in different grades of coarseness; larger grain sizes (typ. 100µm to 250µm) tend to be brighter than the finest grades (~10µm). All are equally suitable for this tutorial, plus blending colours is an option should you want to experiment.
The powder used in this tutorial is 20g of an Aqua Blue at around 30-40µm grain size. 20g is more than enough to do a few full sets of fret markers. This shouldn't cost more than a few dollars/shekels.
Epoxy or Casting Resin
For casting, you need a common clear resin such as an epoxy or similar two-part system. I'll be using ZAP Z-Poxy 30min (PT-39) however you can easily substitute this for a different product such as West System 105, a casting resin such as Alumilite or similar cold curing resin. Have a hunt around the RC enthusiast or crafts casting suppliers and sites; they tend to have plenty of epoxies on stock plus a lot of experience in their application.
Z-Poxy 30min (PT-39) was chosen out of economy and availability. Although designed as a adhering epoxy, that property is not important in this context. The Z-Poxy line also includes a Finishing Resin (PT-40) for fibreglass or carbon fibre layups, which also sets up in 30 minutes. That would also be a satisfactory alternative, however tends to be more expensive.
General DIY epoxy glues for repairing things around the home (those in the two-tube syringe dispensers like Araldite, etc) are a poor substitute at best; a quality epoxy costs about the same as these consumer-grade repair glues, however they don't tend to come in the same small quantities. That said, a good epoxy has many uses around the workshop so is a good investment beyond this one job.
The Z-Poxy 30min was €21,50 for 8fl oz/237ml. That's about 3-4 mouthfuls, however this is not a safe or standard method of measurement. It might seem a small quantity or a high price, but this is enough for several bags of glow powder and it'll run you a load of different jobs. The big ticks are that it dries clear, has a sufficient open time (30mins to gel, a few hours more to fully cure) and isn't finicky if you get the mix ratio slightly out.
For the mould, we're going to use a cheap and commonly available kitchen chopping board made of HDPE (High Density Polyethylene). Unlike most materials, casting resins and epoxies don't adhere at all well to HDPE plus it's pretty simple to machine, making it an ideal choice.
Obviously, most people don't care too much about what material their cheap plastic chopping board is made of and correspondingly, manufacturers don't go out of their way to write it all over the packaging. That said, find the triangular recycling (PIC) mark which identifies the plastic type. Any marked with a "2" in the centre will be HDPE and this might be stamped underneath the PIC. Polypropylene or LDPE can work, however HDPE is a more reliable option and more resistant to epoxies.
The chopping board I used was just over 6mm thick (1/4") and cost me €4 for a large magazine-sized board. Pocket money. Whilst I don't need a mould this size, it worked out cheaper than buying the smaller one which was €1 cheaper. I just ripped it to size on the table saw and kept the spare for future use.
If you want to go the whole hog, more exotic polymers such as UHMWPE (Ultra High Molecular Weight Polyethylene) or PTFE (Polytetrafluoroethylene or Teflon) can be sourced from many plastics suppliers in sheet form. Generally these will be more expensive than more readily-available HDPE however their ridiculously low coefficient of friction makes them fantastic for making epoxy moulds. Ask if they have any free scraps or samples.
The process is relatively simple. Prepare the mould. Mix up one part of your epoxy or casting resin with the glow powder. Add the second component and then pour it into the moulds. Allow it to cure, and push the finished pieces out. Let's look at each stage in more detail.
Making the mould
HDPE is simple to machine using woodworking tools. When drilled, HDPE tends to produce long spirals of swarf which wrap themselves around the drill bit. Whilst not a hazard, it's worth clearing the drill of this swarf every now and again. Drill speeds should be lowered to a very slow speed as HDPE starts to become soft and melty above 80°C/176°F. This can cause swarf to weld itself back to the workpiece. Routing HDPE is similar. The lowest speed possible on the router works a treat, producing small chips and a clean finish.
Round dots are the most common and easiest moulds to prepare; simply drill the HDPE straight through with the appropriate size bit. I set up a simple jig on the pillar drill to cut set of 6,0mm 5,0mm and 2,5mm holes. The jig is simply a back stop made from a flat piece of scrap board which allows the holes to be cut in a neat line. Totally not necessary, however it helps speed up the work and helps make the most of the real estate around the HDPE sheet.
It's worthwhile making more mould holes than you might need. Any unused epoxy can be used to cast spare dots in case any turn out faulty. The mould will be reusable dozens of times, it is a good idea to consider making ordered sets of holes corresponding to marker sizes you commonly use, or may use in future.
To make some rounded side markers, a simple small diameter cutter is fitted into the router. The height is set short of cutting the entire board through.
Halfway is fine and will produce a ~3mm deep mould. That said, I know this router table to be poor, and the top flexes in use. I expect just over 4mm of cut. Thankfully this router table is not mine....
Using a squared piece of scrap as a push stick makes this cut safe since it is too short to run against the fence on its own. Push with the board, keeping the workpiece pressed flush back against it and both pressed against the fence. Once the cut have been made, draw both pieces backwards steadily.
Nice. Two clean rounded-end slotted moulds....and they measured about 4,5mm deep so the table was particularly bendy today....
Progressively moving the fence backwards makes a series of slots into the edge. One or perhaps two of these slots were poor cuts with slight bites into the sides ruining the straightness. I'll black those up with a permanent marker so I don't use those.
Preparing the mould
Clean your mould using a cloth dampened with denatured alcohol. After drying, apply masking tape to the moulds to close them off. For the side markers, create a "dam" by closing the edge up to the corner. Fold the tape underneath and burnish it to the plastic with your fingers.
For the through holes, strips of tape closing the underneath is all that is needed. Again, burnish the tape securely with your fingers.
Mixing the epoxy
Pre-heat the resin and hardener in lukewarm water. This helps to reduce the thickness of the epoxy, allowing for easier working and fewer bubble inclusions.
Wearing nitrile gloves is recommended when working resins. Epoxy resins and hardeners are sensitisers, causing rashes or other nasty things. The more you expose yourself to them, the more likely you are to have reactions. The warnings on the box are no joke. Keep a cloth and some denatured alcohol nearby to clean up any spills or accidental skin contact.
In two mixing cups, measure equal amounts of resin and hardener. Follow the manufacturers instructions on measurement; some are fine by weight whilst some recommend by volume. Stick as close to the the recommended correct ratio as possible. In this case, Z-Poxy 30-min recommends a 1:1 ratio. Experience tells me that there is a little fudge factor either side of this. It's a pretty friendly product to work with. Epoxies like West System 105 (5:1 ratio) tend to be a little less forgiving.
If you are planning on making a very large number of markers, consider splitting the work up into batches. Resins cure chemically, and a byproduct of this process is exothermic heat. Unfortunately, the curing process is also accelerated by heat! Mixing up large batches of curing resin can easily lead to self-sustaining thermal runaway, causing the resin to boil or even catch fire. At best the mixture starts to gel before you're finished working with it.
Measure an approximately equal volume of glow powder into either the resin or the hardener. I haven't decided whether either is a better choice to mix into as of yet.
Incorporate the powder using a stirring stick. The mixture will become thicker and start to fold over itself as the powder is worked in. Draw the mixture over any dry or wet residue, splitting and refolding it until completely smooth and incorporated. Scrape the sides and the bottom to ensure nothing escaped. The resulting mixture should be easy to scrape out of the container, leaving little residue.
Mix this into the second component and again, incorporate fully. Scrape the sides and base of the container to remove any stubborn pockets. The clock is now ticking. For Z-Poxy 30-min the open time (not the cure time) is around 30 minutes. Since we heated the components slightly to make them more workable, this may be a little less than stated. Still, we have more than enough time to mould up several sets.
Time to get to work
Use a kebab skewer or similar, draw a lump of the mixture from the cup. Allow this to drizzle off the end of the stick and into the target mould. It's not too important to be super accurate. Do remember that the clock is ticking! Any under or over fills are no big deal, plus the epoxy will settle in.
A few minutes later, I had all of the mould filled and excess epoxy left over. Wasteful, which is a real shame. I should have made a larger mould set, however I'll have a spooky glowing cup anyway. I'd used the stick to scrape excess over the mould and a cocktail stick to check the smallest dots didn't have bubbles. The warm epoxy flowed nicely and where it was meant to with no bubbles at all. Excellent.
Finish up by taking a craft knife blade (a small rubber squeegee would be good also) to drag excess over and off the surface. I held the blade at about 45° to force excess down into the mould for a better fill. For the side markers, dragging at 45° to the direction of the markers as the blade scraped across helped prevent lifting of the epoxy out of the moulds. When the epoxy starts to set up, it likes to "grab" and try dragging itself out.
Okay, everything is looking good. The epoxy felt as though it was becoming more difficult to work and the excess in the cup was feeling warm to the touch. This is a sign that the curing process has kicked into motion; exothermic heat from the chemical reaction. Time to leave it to chooch.
A few hours later the epoxy was more or less done. Adding fillers like luminescent powders might effect the absolute curing time, however the Z-Poxy 30-min seems like an ultra-hard candy after three hours anyway despite this. The mould was washed in warm water and the masking tape peeled or rubbed off as it soaked. Epoxy is waterproof, so washing doesn't affect the markers.
Poking out the first 6,0mm dot shows a consistent and bubble-free mould fill. This dot is more or less the full thickness of the mould; far deeper than inlays really need to be. Better than too shallow of course!
The easiest method of popping dots out is placing the mould on top of a roll of masking tape or some other flat supportive surface with an empty area in the middle. Popping dots out from the top of the mould seemed more difficult than popping them out from the back.
The side marker lines are a little different. Flexing the mould slightly "cracks" any adhesion between the mould and the epoxy. Persuasion with a fingernail or a flat-bladed screwdriver easily removes them.
The result! One of the smallest (2,5mm) dots had a bubble, however this round saw almost a 100% yield.
Time to start making collections. There'll be piles more where these came from as this used a small quantity of epoxy. The cost of these inlays is a fraction of any commercial equivalents, plus they're far thicker.
After briefly charging the inlays using a lightbulb the inlays glow strongly! Daylight contains more UV which is a better option for charging luminescent inlays. My blacklight LED torch had not yet arrived in time for publication; these can be bought for a couple of dollars on eBay or wherever. Blacklight or UV LEDs and charge luminescent inlays extremely quickly and strongly! Do bear in mind the warnings about exposing your eyes to direct UV light....
Dots can be installed much the same as any other; a hole drilled to the corresponding size and glued in with a drop of cyanoacrylate glue. The epoxy dots respond well to being filed flat before sanding and polishing along with the rest of the fingerboard. The colour is a slightly-off ivory with a hint of green.
UPDATE: The dots are painfully bright after brief charging with an LED blacklight pen:
Remember the pot of waste epoxy? This is how it shines in daylight.
You are not restricted to casting markers in HDPE moulds or using epoxy as a binder for the luminescent powder.
The epoxy mixture works wonderfully cast directly into brass, copper or sterling silver tube to produce a metal outline for the dot. Simply wrap masking tape around the outside of the tube to keep it clean and pour epoxy directly in.
Forum member Chris Verhoeven produced a fantastic video on direct casting of photo-luminescent dots. Rather than casting the markers separately, Chris fills the dot locations with luminescent glow powder and wicks cyanoacrylate glue in to lock up the powder. In addition, lacing the glow powder with Ebony dust creates a faux reconstituted stone look to the finished item.
For a future tutorial, we will look at making more complex moulds for making inlays....stay tuned!
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How To Make Glow-In-The-Dark Fret Markers by Carl Maltby is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.
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