This part of ISO 17226 specifies a method for the determination of free and released formaldehyde in leathers. This method is based on colorimetric analysis.

The formaldehyde content is taken to be the quantity of free-formaldehyde and formaldehyde extracted through hydrolysis contained in a water extract from the leather under standard conditions.

This process is not absolutely selective for formaldehyde. Other compounds such as extracted dyes could interfere at 412 nm.