Substrate Engineering Checklist

QR Code Placement-by-Material & Substrate Guide

Interactive prepress guidelines for printing on glass, metal, wood, apparel, cardboard, and curved packaging. Audit specular glare, ink bleed, and module thresholds.

Clear Glass & Storefront Windows

Glare Risk: Extreme

Contrast & Inking Strategy:

Always print a solid white background flood coat behind the QR code.

Finish & Coating Recommendation:

Use matte anti-reflective vinyl to eliminate specular sunlight glare.

Critical Manufacturing Pitfall:

Never print black modules directly onto transparent glass; passing shadows will destroy contrast.

Pre-Flight Press Checklist0% Ready

Quiet Zone: At least 4-modules unprinted white border verified.Contrast Ratio: Exceeds 4.0:1 (dark ink on light substrate).Artwork Format: Vector SVG or 300+ DPI PDF (no 72 DPI JPG).Specular Glare: Matte finish applied or white flood layer printed.Physical Size: Larger than minimum 20x20mm camera focus limit.

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Substrate Physics: How Print Materials Influence Optical Scanners

In graphic design software, a QR code exists as ideal mathematical black and white pixels. In the physical realm, light behaves according to Snell's law and Fresnel reflection equations. Substrates like clear acrylic, curved glass bottles, and laser-etched metal reflect light unevenly across camera sensors.

The Destructive Impact of Specular Highlights

When an overhead supermarket fixture or sunny window reflects off a high-gloss lamination, it generates a "specular highlight"—a blinding hot spot of 100% white luminance. If this hot spot covers even a few data modules, the camera's auto-exposure circuit dims the entire frame, turning your white quiet zone into a dark gray and causing immediate scan failure.

Frequently Asked Questions About Substrates

Why does printing on glass or clear acrylic require a white backing layer?

Transparent substrates allow background objects, ambient shadows, and indoor lighting to show through. If a customer scans a window code with a dark interior behind it, the camera cannot distinguish the black modules from the background. A solid white flood coat restores a reliable 7:1 contrast ratio.

How do I prevent laser engraved QR codes on wood from failing?

Select a fine-grain, pale wood species such as Baltic birch, maple, or basswood. Run a high-contrast burn setting and ensure the individual module size is at least 0.8 mm so natural wood grain pores do not blend with the modules.

What is ink dot gain and why does it affect cardboard packaging?

Dot gain is the phenomenon where liquid ink absorbs into paper fibers and expands outwards before drying. On porous corrugated cardboard, dot gain can widen dark modules by 15-20%, encroaching upon adjacent white spaces unless compensated for in prepress software.