Discover what mixing or testing could be required to return a penetrant to its original state once it has frozen

Luckily, if using an AMS 2644 Qualified Product List (QPL) approved penetrant from Magnaflux, the answer to this question is very little. Simply allow the penetrant to completely thaw. The penetrant will return to its original, usable state. No mixing or testing is necessary or required. 

AMS 2644 Temperature Stability Requirements  

Nearly all fluorescent and visible penetrants offered by Magnaflux are qualified to AMS 2644. In order to meet the temperature stability requirement of AMS 2644, a penetrant must remain stable after a series of cold/hot cycles. Required testing is as follows: 

1. The penetrant is cooled to -18˚C and maintained for 7 hours. At the end of this 7 hours, the penetrant is allowed to warm to room temperature and examined. The penetrant must return to its original state without being stirred or otherwise mixed. If the penetrant splits or remains hazy and requires mixing, the penetrant does not meet the requirements of AMS 2644. 
2. The penetrant is next heated to 66˚C and maintained for 7 hours. At the end of this 7 hours, the penetrant is allowed to cool to room temperature and examined. Again, the penetrant must return to its original state without being stirred or otherwise mixed. 
3. Each cold/hot cycle is repeated for a total of 2 cold cycles and 2 hot cycles. The penetrant is examined at the end of each cycle to verify thermal stability. 

Thawing Recommendations