Resin Exposure Test: How to Calibrate Exposure Time for Sharp Miniatures
Every new bottle of resin needs its own exposure time. Here's the test print process I run on my Saturn, what over- and under-exposure actually look like on a 28mm mini, and how to dial in the number in one print.
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Exposure time is the setting people copy from a forum post and then never think about again. That works right up until you switch resin, and suddenly your chainmail is a smooth blob and your spear tips are missing.
Here’s the thing nobody tells you when you buy your first printer: the number on the resin bottle is a starting point, not a spec. It was measured on a specific printer, with a specific LCD, at a specific temperature. Your Saturn in a 62-degree basement is not that setup. The gap between “manufacturer recommended” and “actually correct for my machine” is usually somewhere between half a second and two seconds, and at 28mm scale that gap is the difference between a mini that looks printed and a mini that looks cast.
I run this test on every new bottle. It costs one print and about 20 minutes of attention, and it’s the highest-value 20 minutes in resin printing.
If you haven’t finished a full print cycle yet, start with the complete beginner’s guide to resin printing first. And because this involves handling uncured resin in the vat repeatedly, read the resin printing safety guide before you start. Nitrile gloves are not optional here.
Why Does Exposure Time Need Calibrating at All?
Exposure time is how long the LCD shines UV light through each layer to cure it. Too little and the resin doesn’t fully solidify. Too much and it cures past the pixel boundaries it was supposed to stay inside.
That second part is the one that catches people. Cured resin doesn’t stop precisely where the mask told it to. Light bleeds sideways and downward past the intended edge, and the longer the exposure, the further it bleeds. On a large functional print, a fraction of a millimeter of bleed is invisible. On a 28mm character where a chainmail link is a third of a millimeter across, that same bleed erases the detail entirely.
Four things move the correct number:
Resin formulation. Different chemistries cure at genuinely different rates. A standard rapid resin and an ABS-like tough resin from the same brand can be a full second apart.
Resin color. Pigment blocks light. Dark grey and black resins typically need more exposure than a translucent or light-colored resin of the same formulation.
Layer height. A 0.05mm layer needs more light than a 0.03mm layer because there’s more material to cure through.
LCD age and temperature. Screens dim as they accumulate hours, and cold resin cures more slowly. Both push the correct number up over time.
Every one of those is specific to your setup. That’s why there’s no universal answer, and why copying a number off Reddit gets you into the neighborhood but not to the address.
Step 1: Start From the Manufacturer’s Recommended Exposure
Read the bottle. Most manufacturers print a suggested exposure range on the label or publish one on the product page, usually broken out by printer generation (mono LCD vs. 8K vs. 12K/16K).
Enter that number in your slicer and leave everything else alone. Bottom layer count, bottom exposure, lift distance, lift speed, retract speed: none of those are what you’re testing right now, and changing two variables at once means learning nothing from the result.
If your resin doesn’t list a number at all, start at 2.5 seconds for a 12K or 16K mono printer at 0.05mm layers and work from there. That’s a wide-net starting point, not a recommendation.
For where these fields live and what surrounding settings to lock down first, the Lychee slicer settings guide and the Chitubox settings guide both walk through the full profile.
Step 2: Slice a Real Calibration Model
Do not test with a miniature. A miniature tells you whether the print worked; a calibration model tells you why.
Purpose-built calibration models (the Cones of Calibration and the various validation matrix files are the two most widely used) include three things a mini doesn’t:
- Graded positive details that get progressively finer, so you can see exactly where sharpness falls off
- Graded negative features (holes, slots, engraved text) at marked sizes, so you can count how many stayed open
- Thin unsupported overhangs and fine pillars that fail visibly and early at the wrong setting
Slice it flat on the build plate, no supports, no raft, at the layer height you actually print miniatures at. Flat-on-plate is deliberate here: you want to remove orientation and support variables from the result entirely. This is the one time you want the print sitting flat, which is the opposite of how you should be orienting real models.
Step 3: Print It Without Changing Anything Else
Run the print. On most printers a calibration model takes 20 to 45 minutes depending on layer height.
Note the room temperature while it runs. Write it down. If your print space swings seasonally, this number is going to matter later when the same resin behaves differently in January.
That’s true no matter what printer is running it, including flagship machines like the Saturn 4 Ultra: the manufacturer’s number is a starting point, not a finished answer, which is the entire premise of this test. Close enough to print, not close enough to be right.
Step 4: Wash and Cure It Exactly Like a Real Mini
This step gets skipped constantly and it invalidates the whole test.
Uncured and partly cured resin reads differently than finished resin. A print that looks slightly soft straight off the plate can tighten up noticeably after a proper cure, and a print that looks acceptable wet can turn out to have closed every one of its small holes once it’s finished.
Wash it in IPA or water for the same duration you use on miniatures, dry it completely, and cure it for your normal cure time in your wash and cure station. I run a Mercury Plus and give calibration prints the same treatment as anything else. If you’re not sure what your normal cure time should be, err short and check: over-curing makes resin brittle and slightly yellowed, and it’s harder to undo than an extra two minutes under the lamp.
Same process, every test. Consistency in the wash and cure step is what makes two test prints comparable.
Step 5: Read the Print
Now the actual work. Get the print under good light. A cheap set of digital calipers helps for measuring hole diameters, but your eyes and a fingernail catch most of it.
Signs of overexposure
| What you see | What it means |
|---|---|
| Small holes closed or partly filled | Light bled sideways past the mask boundary |
| Fine raised details soft and rounded | Cured resin expanded past the intended edge |
| Recessed detail (chainmail, engraved text) filled in | Same bleed, showing up in negative space |
| Model looks slightly “inflated” or primed | Cumulative bleed across the whole surface |
| Print stuck hard to the FEP | Layers curing past their boundary onto the film |
Signs of underexposure
| What you see | What it means |
|---|---|
| Fine details missing or partly formed | Not enough cure to hold the smallest features |
| Visible gaps or splits between layers | Layers not bonding to each other fully |
| Thin sections fragile or bendy after curing | Incomplete polymerization through the section |
| Print detached from plate or supports mid-run | Adhesion failed before the model finished |
| Surface tacky before curing | Resin never fully solidified |
The single most useful reading is the negative features. Count how many of the graded holes stayed open at their marked sizes and note the smallest one that did. That number is your resolution ceiling, and it moves in a clean, readable direction as you change exposure. Positive detail sharpness is more subjective; hole counts are not.
If your print didn’t just come out wrong but actually failed, that’s a different diagnosis. The print failure troubleshooting guide covers the causes that aren’t exposure at all.
Step 6: Adjust in Small Increments
Move by 0.2 to 0.4 seconds at a time. Not a full second.
At miniature scale, a half-second swing is enormous. I’ve watched a 0.3-second reduction take a model from “chainmail is a texture suggestion” to “chainmail has individual links,” on the same file with the same resin.
Reprint after each change. Yes, this means two or three calibration prints for a new resin. That’s maybe 90 minutes total, against a bottle of resin that will produce dozens of miniatures at whatever quality this number sets.
Stop when the smallest positive details are crisp and the smallest holes are still open. Those two conditions pull in opposite directions, and the correct exposure is the point where they’re balanced, not the point where either one is individually best.
Step 7: Log It
Write it down. All of it:
- Resin brand and product line
- Resin color (this is the one people forget)
- Printer model
- Layer height
- Room temperature during the test
- Final exposure time
- Bottom exposure and bottom layer count
A note in your phone works. So does a text file. What doesn’t work is remembering, because in three months you’ll have tested four resins and they’ll blur together.
I keep mine alongside my pre-print checklist so both get looked at before every session rather than after a failure.
Which Resins Need Retesting Most Often
Some resins are more sensitive than others. In my experience:
Tough and ABS-like resins are the most exposure-sensitive category. Siraya Tech Blu in particular has a fairly narrow window where it holds fine detail without going brittle, and it’s worth the full test rather than a guess.
Dark-pigmented resins (black, dark grey, deep colors) need more exposure than lighter versions of the same product. Never carry a number across colors.
Water-washable resins often have a different curing profile from standard resins and frequently need retesting even when switching within the same brand. The water-washable resin guide covers the other trade-offs involved.
Standard rapid resins in light grey are the most forgiving and usually land closest to the manufacturer number. If you’re only going to skip the test on one thing, skip it here.
If you’re still picking a resin, the best resin for miniatures roundup breaks down which formulations hold detail best, and the best resin for painters guide covers which ones take primer and paint well after curing.
The Short Version
Exposure calibration is one print and one number, and it decides how much of the sculptor’s work actually survives onto your build plate. Manufacturer numbers get you close. A calibration model, a proper wash and cure, and two or three 0.3-second adjustments get you the rest of the way.
Run it once per resin, log the result, and stop guessing. The detail was always in the file. This is how you get it out.