A hot sheet reproduces the surface it contacts. Tool grain, machining marks, wood pores, repairs, corrosion, and contamination can therefore appear directly on the finished part.
The level of transfer depends on material temperature, pressure differential, sheet finish, and contact time. A surface that looks acceptable on the cold mold may become obvious on a glossy formed part.
Correction
The part defect should be compared with the tool under directional light. The mold must be cleaned before refinishing so embedded contamination is not polished into the surface. The required finish should then be defined: high gloss, controlled matte, or a specified texture.
Porous or low-durability tool materials may need sealing or replacement for production. Sanding every tool to a smooth finish is not always correct because some processes require micro-texture for air evacuation. Surface quality and venting must be designed together.