One of the most direct ways to verify whether ceramic frit ink has been properly fused into a glass panel is the knife scratch test. After firing or tempering, a hardened steel blade is drawn across the printed surface under measured pressure. If the ink stays put, firing was correct. If it lifts, the firing curve, ink layer, or substrate prep needs adjustment.
This article walks through how we conduct knife scratch testing on samples printed with Moyan ceramic ink, what to look for, and how the results map back to production decisions.
Why a Knife Scratch Test Matters
Ceramic frit ink works because the glass-frit pigments melt during firing and chemically bond into the substrate surface. A correctly fired panel has ink that is mechanically continuous with the glass — you cannot peel it because there is nothing to peel. An under-fired panel still has the ink sitting on top, vulnerable to abrasion, cleaning, and edge lift over time.
For B2B buyers evaluating ceramic ink and glass printing machines, a simple knife test on sample panels reveals whether the ink-machine-firing combination is delivering true ceramic adhesion or just looks good before service.
Test Setup We Use
- Sample — a printed glass panel that has completed the full firing or tempering cycle (typically 650–720°C for tempering)
- Blade — a hardened steel utility blade or scalpel, fresh edge
- Test areas — at least three locations: solid color block, fine line/text, and an edge close to the panel border
- Pressure — moderate hand pressure, the same force you would use to score cardboard
- Stroke — single straight pass across each test area, perpendicular to any line work
What a Pass Looks Like
On a properly fired panel, the blade leaves a faint shiny mark on the ink surface but no ink transfers to the blade and no color removes from the panel. Wiping the test area with a soft cloth shows the ink is intact. Held against light, the scratch is visible only as a polish line in the surface, not as a void in the printed graphic.
What Failure Looks Like
- Ink flakes off — firing temperature was too low, ink never fused. Increase peak temperature or hold time.
- Ink smudges or transfers to the blade — partial firing, surface still soft. Check kiln calibration.
- Color lifts at panel edges only — surface preparation issue at the edge, or thermal stress concentration. Review pre-print cleaning and panel handling.
- Print scratches deep but stays bonded — firing is good, but ink layer is too thick. Reduce ink density in RIP profile.
Pairing the Knife Test with Other Verification
The knife test is fast and repeatable on the production floor, but for project specifications it is usually paired with:
- Cross-hatch tape adhesion test (ASTM D3359) — quantitative grading from 0B to 5B
- Pencil hardness test (ASTM D3363) — measures surface hardness from 6B to 6H
- Boiling water immersion — 2 hours at 100°C, then knife test again
- UV exposure cycle — for outdoor architectural and signage applications
For Moyan customers, we run knife and cross-hatch testing on every sample we send before customer trial, and we provide the test photos with the sample shipment. This lets your QC team verify before machine commissioning that the ink-firing-substrate combination is correct for your production line.
Apply This to Your Project
If you are evaluating ceramic ink suppliers or commissioning a glass printing machine, ask the supplier to run a knife scratch test on a sample of your substrate at your firing curve. A quality supplier will agree without hesitation. Send us your substrate type, firing curve, and target application, and we will print, fire, and test a sample panel for evaluation.
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