# Marks on eggshells: when do they become a defect?

> Cage and belt marks are scratches, scuffs and light abrasions caused by handling. Under the American definition of a dirty egg, a mark with no adhering material is not dirt. But Class A requires a smooth, clean and intact shell (RIISPOA, art. 225), so a mark becomes a defect when it alters the shell or leaves material on it. Lighting changes how these marks look, and the team needs a written criterion.

Updated: 2026-10-09 · URL: https://vigiovo.com/en/resources/shell-marks-and-scuffs · Português: https://vigiovo.com/recursos/marcas-na-casca.md

## Key takeaways

- Under the American definition, a mark with no adhering material is not dirt (7 CFR 57.1).
- Class A requires a smooth, clean and intact shell (RIISPOA, art. 225, I), so marks that alter the shell take the egg out of that class.
- The standard does not list types of mark, so the team needs a written criterion for each case.
- Raking light and reflections make shallow marks look darker on camera.

## What are cage and belt marks?

Cage and belt marks are changes an egg picks up when it touches wire, the edge of a tray, rollers or other eggs during collection and grading. They show up as fine scratches, scuffs, small abrasion marks or areas of altered gloss on the shell.

Not every mark is the same. A line that only grazes the surface is different from a patch of material that has stuck. The difference matters because the definition of a dirty egg treats adhering material in its own way.

## Is a mark on the shell dirt?

Not always. Under the American definition, a [dirty egg](https://vigiovo.com/en/resources/glossary#dirty-egg) is one with an unbroken shell and adhering dirt or foreign material (7 CFR 57.1). A scuff with no material on it does not fit that definition, but a mark with material stuck to it, such as faeces, soil or yolk, does.

In Brazil, the test is the clean shell of Class A (RIISPOA, art. 225, I). The practical question is whether material sits on the shell or whether the shell itself has been altered. The two cases lead to different outcomes, and [faecal contamination](https://vigiovo.com/en/resources/faecal-contamination-on-eggs) follows its own rules.

**Marks and dirt: how they usually appear (practical judgement, not a legal test)**

| Type | How it appears | Classification |
| --- | --- | --- |
| Scratch or scuff | A fine line or abrasion, with no material on the shell | Depends on the alteration; judge against a smooth, intact shell (art. 225, I) |
| Friction mark | A dull area or one with a different gloss, with no material | Judge the shell's final appearance and record the criterion |
| Adhering material | A stain in a colour unlike the shell, such as faeces, soil or yolk | Dirty egg, outside Class A (7 CFR 57.1; art. 225, I) |

The table is a practical reading of the definitions, not a rule of the standard. That is why the criterion has to be written into the line's procedure.

## When does a mark become a defect for Class A?

A mark becomes a defect for Class A when it leaves the shell without the features of art. 225, I: smooth, clean and intact. A mark that removes the cuticle, alters the surface or breaks the shell no longer meets the text of the standard, even when there is no dirt.

When a mark does not break the shell and has no adhering material, the case calls for judgement. The standard does not list types of mark, so the team sets in writing how far a mark is acceptable for Class A.

## How does lighting change the look of a mark on camera?

Lighting decides what the camera sees. Under raking light, any relief or scratch casts a shadow and looks like a dark mark, even when it is only a fine line. Under diffuse light, the same shell looks more even and the contrast drops. That is why one mark can be accepted under one light and rejected under another. More detail is in [lighting for egg inspection](https://vigiovo.com/en/resources/lighting-for-egg-inspection).

Reflections also mislead, because a smooth, wet patch can look lighter or darker than it is. Before fixing a criterion, test the mark under your line's real light, not only on the bench. A surface camera also cannot see beneath the shell, so a surface mark and an internal crack are different problems.

## How do you set a mark criterion for your line?

Set the criterion with real photographs before the line runs. The aim is that the same mark always gets the same outcome:

- Gather photographs of marks that are accepted and marks that are rejected, under your line's light.
- Separate adhering material from changes to the shell itself.
- Write the outcome for each case, including when the egg leaves Class A.
- Review the criterion with the quality team whenever the batch, the light or the camera changes.

This step makes grading auditable: whoever looks at the egg and whoever reads the record reach the same decision. To compare inspection methods, see [candling or computer vision](https://vigiovo.com/en/resources/candling-vs-computer-vision).

## Frequently asked questions

### Does a cage mark on the shell make the egg dirty?

Not necessarily. A scratch with no adhering material does not fit the definition of a dirty egg (7 CFR 57.1). However, Class A requires a smooth, clean and intact shell (RIISPOA, art. 225), so the mark can take the egg out of that class. The decision depends on how the shell has been altered and should follow a written criterion.

### Can a belt mark be mistaken for a crack?

Yes. A fine, elongated scratch looks like a visible crack, and raking light makes this worse. The camera should therefore assess the shape of the line and its depth before classifying. Hairline cracks don't show on the surface and need candling.

### Does Class A accept any mark on the shell?

The standard asks for a smooth, clean and intact shell (RIISPOA, art. 225, I), but it does not list types of mark. The team sets the limit, with a written criterion and reference photographs. An egg with a broken shell or adhering material does not qualify for Class A.

## Sources

- [Decreto nº 9.013/2017 (RIISPOA)](https://www.planalto.gov.br/ccivil_03/_ato2015-2018/2017/decreto/d9013.htm), Presidência da República (Brasil)
- [7 CFR § 57.1 Definitions (Inspection of Eggs)](https://www.ecfr.gov/current/title-7/subtitle-B/chapter-I/subchapter-C/part-57/subpart-A/section-57.1), U.S. Electronic Code of Federal Regulations

## Read next

- [Shell colour variation isn't dirt: how to tell them apart](https://vigiovo.com/en/resources/shell-colour-variation.md) (Explainer, 2026-10-09): How to separate natural shell colour and speckling from adhering dirt in egg grading, and why comparing each egg with its own shading avoids false dirty grades.
- [Faecal contamination on eggs: risks and correct destination](https://vigiovo.com/en/resources/faecal-contamination-on-eggs.md) (Explainer, 2026-10-09): Why faecal dirt makes an egg unfit as it is, when washing is mandatory in Brazil, and what to do with dirty eggs that are also cracked.
- [How to identify cracked eggs: types, methods and rules](https://vigiovo.com/en/resources/how-to-identify-cracked-eggs.md) (Guide, 2026-10-09): What a cracked egg (check) is, how it differs from a leaker, which methods detect each kind of crack and where cracked eggs must go under the regulations.

## How Vigiovo helps

Vigiovo grades eggs on the conveyor as clean, dirty, cracked or unverified, in real time, with deterministic computer vision: every decision comes with the measurements behind it, on an ordinary CPU. https://vigiovo.com/en/how-it-works.md

4 min read.