Yellowing caused by oxidation or light ageing does not mean the sole was insufficiently cleaned.
Check first
- Is yellowing concentrated in clear or white material?
- Does the colour remain largely unchanged after surface cleaning?
- Is there brittleness or powdering?
- How do the two shoes and exposed versus protected areas compare?
Working sequence
- Perform suitable routine surface cleaning first.
- Assess whether the material itself has changed.
- If colour restoration is proposed, weigh its value and risks.
- Explain possible yellowing recurrence and suitable storage at handover.
Strong oxidising or reducing products may affect adhesives, prints and material life. Do not promise permanent freedom from yellowing.