Printed paper cup color comparison can produce conflicting approvals when the supplier and buyer use different lighting. Two samples may match under one source but differ under another, a phenomenon called metamerism. An uncontrolled office-light comparison is a weak basis for changing a production print recipe.
Agree the physical reference, viewing condition and color acceptance method with the buyer. This guide addresses sample comparison and evidence collection. It does not assign a universal color-difference tolerance or replace the applicable print specification.
Diagnostic decision table
| Observed disagreement | Check first | Keep in the record |
|---|---|---|
| Match in one room, mismatch in another | Lighting-dependent match | Identified light sources |
| Mismatch changes when cup is rotated | Gloss and viewing geometry | Sample angle and viewing position |
| Instrument passes, visual review fails | Measurement and viewing conditions | Mode, backing and illuminant |
| Phone images disagree with physical samples | Camera and display processing | Physical reference identity |
Establish a stable physical reference
Use the approved production reference or agreed color standard with a clear identifier and revision. Check for fading, abrasion or contamination before comparing new work. Do not treat an old cup displayed in sunlight as equivalent to a protected retained master. Record which reference the buyer actually approved.
Compare the same printed region on samples with comparable surface condition. If one sample is a flat proof and the other a formed cup, recognize that curvature changes the viewing geometry. Decide whether the approval concerns the flat print, finished cup or both, and preserve the relevant samples for each stage.
Make the viewing condition reproducible
Use the agreed controlled-lighting arrangement and maintain it according to the equipment instructions. Keep the surroundings neutral and avoid mixing the comparison light with strong ambient illumination. Record the selected source and viewing geometry so the buyer and printer can repeat the observation.
Place the samples consistently and compare them side by side. Rotate or reposition them only as a deliberate check, noting whether gloss or shadows drive the apparent mismatch. A reflected highlight on one curved cup and not the other can look like a color problem even when the printed regions are comparable.
Use a second light source to investigate metamerism
X-Rite describes metamerism as a match under one light source that does not remain a match under another. After assessing the samples under the primary agreed condition, use an identified secondary condition if the buyer requires that check. Record whether the pair separates and which colors show the largest visual change.
Do not repeatedly change the recipe to satisfy whichever room is being used that day. A second-source mismatch is evidence to review the ink, substrate and specification relationship. The appropriate response depends on the agreed application and material system, not solely on a photograph showing that one cup looks warmer in a different room.
Reconcile the instrument and visual methods
When using a spectrophotometer, record instrument identity, measurement mode, aperture, backing, illuminant and observer settings relevant to the agreed method. Keep these consistent between the master and trial. Different modes or backing conditions can produce different results without any production change.
Measure a flat retained print region if that is the validated method, and separately assess the finished cup where required. Avoid forcing a curved sample against an instrument in an unvalidated arrangement. A small numerical difference under one specified condition does not establish a visual match under every light source or viewing angle.
Resolve approval with a documented comparison
Create a concise record identifying master, trial lot, printing setup, substrate, lighting and measurement conditions. Describe whether the mismatch is present under the primary condition, appears only under the secondary condition or changes with geometry. Attach photographs as location and arrangement evidence, while retaining the physical samples for actual color judgment.
Send HANNAI the record when reviewing a printing configuration or process complaint. Ask the buyer to confirm the intended approval condition before revising a stable recipe. Once a correction is agreed, compare the new trial under the same method and check that resolving one brand color has not degraded other important parts of the artwork.
Related equipment and next checks
Review the digital packaging printing equipment and the related guide to instrumental print-color control. The Engineering Notes archive connects these checks with wider machine planning.
Technical reference
- X-Rite color guide and metamerism definition — general reference; confirm applicability to the installed equipment.
Frequently asked questions
Can a phone photograph approve print color?
Use it for documentation, not as a substitute for the agreed physical and instrumental comparison.
Does one matching light source prove all lighting will match?
No. A metameric pair may separate under another source.
Should flat proofs and curved cups be compared identically?
Define and control the geometry appropriate to each approval stage.
Is there one universal acceptable color difference?
Use the buyer-approved specification and measurement conditions.
Review the evidence with HANNAI
Send your machine model, component identification and the observations described in this guide. Include the drawing or material reference and any before-and-after measurements so the required next check can be identified.