Reading a Shallow Depression on an Eyeshadow Lid: Sink Mark or Handling Impression?

A shallow depression on a molded eyeshadow lid deserves a careful description before a cause is assigned. A sink mark can relate to local molding shrinkage; a handling impression can result from later contact or pressure. Their appearance may overlap, so the useful distinction comes from geometry and sample history together.

SamBound sample showroom. Context photograph.

Why an internal rib can influence the outer face

Where a rib or boss joins a wall, the junction can contain more material than the adjacent area. A thicker region can cool and contract differently. If contraction is not adequately compensated during molding, the outer surface may draw inward and leave a depression. Protolabs' molded-part design guidance identifies heavy rib and wall junctions as a potential source of sink.

That mechanism makes the relationship between the depression and internal geometry worth checking. It does not mean every eyeshadow lid has a rib, every rib causes sink, or every depression opposite a rib has the same cause. Material behavior and molding conditions also affect the outcome.

Use geometry as a clue, not a verdict

Compare the affected location with the actual part and drawing. An exterior product photograph cannot establish hidden wall thickness. Where samples from more than one cavity are available, identify them correctly and compare corresponding locations under consistent lighting. Reflective decoration can make a small contour change more noticeable without showing when it developed.

Repeated position can support a molding-related investigation, but it is not decisive. A fixture or repeated packing contact can also mark the same location on several parts. Conversely, sink severity can vary with processing conditions, and a freshly ejected part may not show its final cooled shape immediately.

Find the stage at which the change becomes visible

Retain suitable samples after molding and conditioning, after decoration, after assembly and after packing. Compare their surface profiles or images using an agreed method. Establishing the earliest stage at which the feature is present is stronger evidence than relying on whether the mark looks smooth, sharp or white.

If a molding contribution is supported, the technical review can consider local geometry, material, packing and cooling. If the change appears after a handling step, examine supports and contact conditions at that stage. More than one contributor may be present; a geometric explanation should remain open to contrary sample evidence.

SamBound New Material Technology Company Ltd. presents eyeshadow packaging under the Sambound name at sambound.com. This is a general explanation for reviewing molded compact components, rather than a report of a defect in an individual Sambound model. A shared description of location and process stage helps keep development discussions precise.

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SamBound New Material Technology Company Ltd.