UV resin
One part, no hardener, no measuring, and set in about a minute. It is a genuinely different product from two-part epoxy, and its limits are not the ones you would guess.
UV resin is a one-part resin that stays liquid in the bottle until light hits it, then sets in 60–180 seconds under a lamp. It works in layers of 1–3 mm and no thicker — the resin absorbs the light that cures it, so a deep pour skins on top and stays liquid underneath permanently. That makes it right for jewelry, charms, bezels and thin coats, and wrong for anything you could call a casting.
UV resin and epoxy resin share a word and almost nothing else. Epoxy is two liquids that react with each other in fixed proportion; UV resin is one liquid that does nothing at all until it is hit with light of the right wavelength, and then sets in under a minute. There is no hardener, no ratio to get wrong, no pot life and no window in which you have to work — you can leave the bottle open on the table and come back to it tomorrow, as long as the room is not sunlit.
That convenience buys a hard limit. The resin absorbs the very light that cures it, so the light gets weaker the deeper it goes and stops working entirely at somewhere around 3 mm. A thick pour does not cure slowly — the top sets into a solid skin and the resin underneath stays liquid, permanently, and no amount of extra lamp time reaches it. That is a completely different failure from the depth ceiling on an epoxy, where the risk is heat rather than light.
So the two products divide cleanly by size. UV resin is for jewelry, charms, bezels, keyrings and thin repairs — small work, finished in an evening. Anything with a real thickness to it wants table top / coating epoxy or deep pour / casting epoxy, and the epoxy calculator will size that for you.
What each depth actually costs you
A 25 mm bezel filled to four different depths, at 2 mm a layer. The volume barely moves and the lamp time multiplies, which is the whole argument: past about 3 mm you are paying in evenings for something a two-part casting resin would do in one pour. Prices at $11 per 100 ml, which is what UV resin costs and roughly five times what epoxy does by volume.
What it is for, and what it is not
The thing it is genuinely best at, and where the whole cluster's demand sits — a pendant is done in a minute, and the piece is handled and finished the same evening rather than three days later. Jewelry mold, 12 cavities takes about 36.0 ml in total and roughly 2 min–6 min of lamp time.
Sealing a porous surface, filling a scratch, tacking a bail onto a pendant, doming a sticker or a cabochon. Anywhere a thin layer has to be set immediately and clamped by nothing, UV resin does something no epoxy can.
Not a matter of patience or lamp power — light does not reach the bottom, so the middle stays liquid however long you run it. Anything past about 10 mm should be deep pour / casting epoxy, which pours it in one go, cures right through and costs a fraction as much per millilitre.
What actually decides whether it cures
UV resin absorbs the light that cures it, so the light gets weaker the deeper it goes and stops working at somewhere around 3 mm. Past that the top sets into a solid skin and the resin underneath stays liquid — and stays liquid however long the lamp runs, because the light is no longer reaching it. Build up in layers of 1–3 mm and cure each one.
Anything that blocks light — a heavy mica load, white pigment, thick glitter — stops the reaction at whatever depth the light stopped. This is the one rule in this craft with no working around it: if you want a solid opaque casting, it has to be a two-part epoxy.
Lamps are sold at 365 nm and 405 nm, and a resin formulated for one may barely respond to the other. Most modern nail lamps emit both, which is why they work for almost everything; a cheap single-LED torch often does not, and is the usual reason a piece comes out soft.
Oxygen in the air stops the very top few microns from setting, so a thin sticky film across the whole surface is expected rather than wrong. Wipe it with isopropyl alcohol, or cure the piece under a sheet of acetate or in a covered box and the film does not form at all.
On a bright day a thin piece cures in ten to thirty minutes; in the winter it may not cure at all, and a piece cured half in shade will set at two different rates and warp. It also worsens the tacky film, because a slower cure means longer in contact with air.
UV resin is for small work that is handled and replaced, not for a table someone keeps for twenty years. Anything you intend to sell as heirloom-grade should be epoxy.
Working with it
Uncured UV resin is a skin sensitiser and the sensitivity is cumulative — someone who has handled it bare-handed for a year can develop a reaction that does not go away. Nitrile gloves, every time, from the first bottle.
1–3 mm at a time, 60–180 seconds under a mains lamp for each. A keychain torch takes several times that and often never quite gets there. Do not try to save time by pouring two layers and curing once — that is exactly the failure this whole page is about.
Once the lamp goes on the piece is finished, bubbles and all — there is no window in which to fix it. A quick pass with a lighter held well back, or a toothpick, or simply letting it stand for a minute, deals with most of them. UV resin is thicker than epoxy and holds its bubbles more stubbornly, so warming the bottle helps.
There is no window in which to adjust anything. Once the light is on, the piece is finished — a bubble, a hair or an inclusion sitting slightly wrong is now permanent. Get it level, get it clean and look at it properly first; the cure itself is the fast part.
An opaque bottle in a drawer lasts a year or more. A clear bottle on a windowsill sets solid, and there is no recovering it. The same goes for whatever you decant into — a clear pipette left out on the table cures shut.
Do not look into the lamp. These are genuine UV LEDs and staring at one is the same argument as staring at a welding arc.
Size a UV pour, or an epoxy one
Pick UV resin in the system list and the calculator answers in layers and lamp minutes rather than in pours — its own arithmetic, not the epoxy one. Pick either two-part system and it splits the mix into resin and hardener instead.
Open the calculator →Print the pour-depth card
Maximum pour depth and cure windows by resin type — the number that cracks a casting. Free.
Estimates, not advice. Every figure on this page is computed from published reference values and standard measures, so your own inputs, equipment and conditions will move it. Nothing here is professional advice — talk to a qualified professional before acting on it.