Design

A 'Lumascus' Ring Experiment

Detailed process of a lume-inlaid Damascus steel ring prototype.

Joseph Coston

Sep 2, 2024 — 14 min read

The finished prototype Damascus steel ring with luminescent inlay.

I love things that glow in the dark. There is something about the ability to store up light energy only to release it as light again later that feels like IRL magic. As an artist, I am constantly looking for new ways to incorporate luminescent compounds into my works. A lot of the things I make are interactive or wearable, and I think finding ways to make my art emit light in some fashion adds a lot to the experience of holding, examining, and interacting with my pieces.

Jewelry and Rings

I like making many different types of jewelry but constantly return to the ring as an ideal medium. Jewelry, as an artistic medium, is necessarily wearable which allows the owner to appreciate the piece more deeply and more constantly than do many other forms of art. Paintings and sculptures become a part of the environment in which they are displayed but jewelry is much more intimate, adorning the individual. Rings are an ultimate medium, for me, as they not only allow others to admire the piece, as pendants and earrings do, but the wearer may appreciate their own art as they wear it, as well. I don't know about others, but I often forget how much time I spend looking at my own hands until I notice something pretty adorning one of my fingers.

If a material concept can be turned into a ring (lathe pun, intended) then it can be worn and appreciated by the wearer in a wide variety of environments, and conditions.

An Acidic Accident

The idea to combine Damascus steel and luminescence first arose after an accident with etching layered titanium and zirconium mokume gane, sometimes called 'timascus', 'mokuti', or 'zircuti', depending on the artist. (Mokume gane is the Japanese technique of forge-welding layered metals to achieve a wood-grain appearance, which includes both timascus and Damascus techniques.) I had flame-anodized the piece too long and had achieved a color palette that I did not care for, so I had wanted to acid-etch away the anodization and start over. I ended up leaving the ring in the acid for far too long, rendering the surface deeply pitted and crystalline. While it was not the final appearance I was going for, I thought it was plenty interesting nonetheless; a happy accident.

Images of the timascus ring, before (top) and after (bottom) the acid etch.

Layers and Lume

I was intrigued by the severeness of the pitting, however, as I had not known that such a drastic contrast in height could be achieved in mokume using acid, alone. I wondered if it would be possible to exaggerate the pitting to the point that the valleys could be filled in with another material while the peaks were polished flush. Of course, befitting my tendencies, the material to add would be luminescent.

Phosphorescent pigment powders, often referred to simply as 'lume' for their categorization under photoluminescent compounds, are a great way to add a glow-in-the-dark effect to many art projects. I use them often in my resin projects and have added them to paint and blown glass before, as well. Being a power, the question often becomes "how can I incorporate lume in this particular situation?" since the powders alone have nothing to hold them in place.

Here, it is easy to see how the lume sank to the bottom when added to these resin pours (which have been turned upside-down for illustrative purposes).

The trouble with lume powders is that they are dense and often sink to the bottom of resins before the resins can fully set. Workarounds do exist, such as adding the lume after the resin is partially hardened, using thickening agents, or using faster-setting resins, but all techniques have various downsides and can be somewhat unreliable.

Some other resin rings where the lume separated out at the bottom, though to somewhat of a lesser extent.

The difficulty often lies in getting the lume to go where you want it to go and stay there. With many resins, the lume will often sink to the bottom of a pour before the resin can solidify and suspend the lume in place. Many paints require primers to adhere successfully to metal, and there would be no room for such measures in the tiny details of the pitting in the Damascus. I eventually settled on a heat-and-dip enamel as it was advertised specifically for use with metals. It was marketed for use in applications such as fishing lures and the like, able to adhere strongly to metal surfaces with a little bit of applied heat. I thought this method would be best since it seemed like such an enamel was formulated with applications like mine in mind, though I will go over some of the difficulties I experienced, later on. Additionally, enamels are generally harder than epoxy resins and will hopefully bear more wear and tear. Rings see a lot of abuse, residing on the hand.

Stainless Damascus Steel

While I could attempt to perform this technique using timascus, I was not confident the experiment would be successful on my first try. Titanium and related materials are rather costly, exotic, and tend to be more difficult to work with than other metals (titanium is named after the Titans). I would rather not risk wasting expensive materials on a new technique I was testing out for the first time. If the lume application did not work out, I expected it would be relatively difficult to salvage the piece.

I settled on stainless Damascus steel for the experiment as, while still not cheap, I could feel more comfortable taking greater risks with this material. I would only forfeit a couple dozen dollars as opposed to some hundred-odd dollars if I had to junk the whole piece. I also only needed hydrochloric acid for the etch stage. If I needed to handle a lot of acid for many etch stages, I would prefer using HCl to the nastier HF needed for timascus.

An Aside About Acids

While I was able to acid-etch the timascus quite severely, I was only able to do so using a relatively hazardous solution containing, among other things, Hydrofluoric acid (HF) which is generally known to chemists as a compound to avoid; on contact with the skin, HF is capable of causing permanent nerve damage faster than it can be perceived and eventually migrates to the skeleton and directly attacks the calcium in one's bones. It also tends to attack the materials commonly used for storing chemicals and performing chemistry, such as glass and many plastics (polypropylene is a notable exception). I do not enjoy working with chemicals like HF.

While still a dangerous acid, Hydrochloric acid (HCl) is somewhat easier to work with, less toxic, and all-around less scary. It can be handled with relative safety using only standard lab equipment and PPE. As stainless steel can be etched using only HCl, it is a better choice for a project involving heavy amounts of etching.

HF gets a 4 for lethality in the 'health' quadrant of the hazard diamond; HCl only gets a 3. While both are dangerous it is important to know your chemicals.

The stainless steels I chose are 304 and 316, as they are relatively cheap and easy to forge-weld (though I commissioned the bar stock from a Ukrainian blacksmith that has since disappeared from Etsy). I also chose that combination specifically because 316 is more corrosion-resistant than 304, especially in chloride-rich environments, due to the addition of molybdenum. The relative differences in corrodibility would allow the two metals to form a galvanic cell in a HCl acid solution; one of the alloys would act as a sacrificial anode for the other and allow for half of the layers to etch faster than the others, resulting in deep pitting over time.

Fabrication

The process of realizing this concept would take several stages; rough-cutting material, turning the piece to the desired rough dimensions, acid etching, cleaning, enameling, final machining, and polishing.

Turning a Basic Band

The first step was to turn a basic band-style ring on the lathe from the Damascus round stock I had. I wanted to go for a relatively simple shape and let the patterning and wood-grain speak for itself. I wanted to use the lume to accentuate the grain without any distracting band geometry, at least for this first attempt. I may do some more interesting things with shape if I continue to refine the technique.

The basic shape was achieved with a small bench-top lathe. The grain pattern is barely perceivable at this point but will soon be revealed by the acid etch.

I elected not to polish the ring at this stage since I was about to essentially obliterate the surface with acid; I only did some pre-finish sanding. I had decided that while the outside would be etched, the inside of the band would be left relatively untouched. I wanted the features of the ring that would be felt directly upon the wearer's skin to remain smooth and unblemished for the most comfortable wearing experience. No matter how beautiful a piece of jewelry, causing discomfort would make the piece less wearable.

By this stage, the internal dimensions of the ring were already tuned for the ring size I was targeting, so to protect the inside of the band I applied several coats of clear top-coat nail polish. I theorized that the organic polymer would act as a relatively corrosion-resistant physical barrier to the HCl since the acid solution would be inorganic. I'll refer to the nail polish as 'resist' from here on, since that is the common nomenclature for its role in this application, resisting the etchant.

Intentional Acid Etching

The ring after its first coat of resist. I took care with my brush strokes to only hit the inside of the ring.

After waiting a few hours for the polish to cure thoroughly, the ring got a detailed cleaning with dish soap and water, as well as some careful attention with a razor blade in areas that got nail polish when they weren't supposed to. Ready for etching, I fully submerged the prepared piece in a ~25% concentration aqueous HCl solution. It remained there for 2.5 hours.

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While the piece was etching, the reaction released fumes, necessitating ample ventilation.

The etching and pitting were not nearly as deep as I desired for the purpose of inlaying lume. It became clear the etching process would take longer and involve more stages than I had anticipated. The type-304 steel did take on an attractive crystalline surface finish, however.

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The piece after only 2.5 hours of etching and a good rinse/cleaning.

While the effect of a light etch was quite nice, giving a crystallized appearance, it was not what I was going for in this experiment. Unlike the etching process with timascus which will go until most of the acid is consumed, the stainless Damascus etching process creates a passivating layer of oxides that make the reaction slow down over time, even before all the HCl is gone. I ended up needing to repeatedly remove the piece from the etch and wash it off, scrubbing to mechanically dislodge the oxides and reveal more corrodible metal before returning it to the etch. I would like to congratulate metallurgists for engineering such a pair of great, corrosion-resistant steel alloys, but in the end their efforts were unable to resist my determination. Speaking of which, the resist was also affected by the etch solution, requiring me to repeatedly reapply fresh coats between etch sessions.

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After a total of about 24 hours submerged in the etch, spread over 8 separate sessions, this was the result.

In the end, the piece spent a total of around 24 hours submerged in the acid etch. I was not too scientific about it, I just kept going until I felt like I had pitting deep enough to provide sufficient space for the lume inlay. I went off instinct to determine when to stop etching.

Some nicer photographs of the piece after the final etching stage. Notice how deeply the type-304 was etched in contrast to the type-316. The differences between the fine-grained texture of the 316 and the courser 304 are also noteworthy.

Next time I do this, I would like to examine the crystal grain structure of the etched steel under a microscope, as the results were fascinating. Some soap, water, and scrubbing brightened up the surface after the final etch left it grey-black. Nevertheless, it was time to move on to the next phase.

Applying Enamel

With the etching and cleaning done, I could apply the combination enamel and lume using the heat-and-dip process. Pretty straightforward: the piece was heated with a torch to around 500°F then dipped in the powdery enamel. The hot piece melted the powder on contact, forming a durable luminescent layer over the whole outside of the ring.

Right after the enamel dip, the coating was quite thick and would need to be dealt with.

I chose orange enamel for what I thought would give a fiery incandescent-looking glow effect, which turned out to be a mistake. For those less-appraised of color theory, the color brown can be considered a dark shade of orange. I have seen this happen with orange before in my art under different circumstances and should have been able to predict this would happen here as well but still made the mistake. The end product, after the final removal of excess enamel and final finishing, was a combination of silver and greenish-tinged brown.

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The crystalline surface of the type-304 is still visible through the enamel which is nice.

While I was hoping for more vibrant colors, the result ended up being more earth-toned.

The Lume in Different Lighting

While the piece is somewhat subdued under natural daylight lighting, it looks fantastic under UV blacklight conditions and even looks rather good in the dark. Oddly enough, while the enamel definitely appears orange in high concentrations, when reduced to a fine inlay it appears much greener. It is highly likely the enamel itself contains a fluorescent orange pigment paired with green lume since green formulations are the most efficient.

Drag the slider to compare images taken under white light and in darkness:

The dark photo in this comparison was taken under UV blacklight:

Possible Improvements

I don't completely dislike the brown, which could be mistaken for a tasteful patina of rust at a distance, but I would still have preferred either a brighter orange or a cooler color like green or blue. Furthermore, the choice of heat-and-dip enamel was, in retrospect, a mistake. Being a thermo-polymer enamel, I had expected the melting point to be quite high for durability, but the opposite was true. The melting point was so low, in fact, that the friction of sanding and buffing often generated sufficient heat to slightly liquefy the surface of the enamel and reset the finishing process back to square one, an incredibly annoying property to work around. It was so finnicky to polish that I inevitably settled for a matte/brushed finish on the final ring in order to avoid the high-friction conditions of high-grit polishing needed to achieve a high-shine surface.

For both colors and enamels, I'll know better for next time.

Thanks for reading,
~Joseph