Blue Stains on Newly Pressed Oak Veneered Panels

Steel platens can make a blue stain on Red Oak. Here's advice on prevention and cure. October 29, 2012

Question
I do a lot of veneer layup (mostly red oak veneer) on plywood, MDF, and blockboards. The problem I am encountering constantly is the presence of blue stain (after hot-pressing the panel) in areas where there is putty on the panel surface (due to defects on the face veneer).

What is the most effective way to prevent blue stain from appearing when dealing with red oak veneer? Do we need to stack the panels after hot pressing to prevent moisture buildup (and causing the blue stain)? Also, what are the best ingredients for wood putty?

Forum Responses
(Veneer Forum)
From contributor D:
Are you pressing using metal platens? Try separating panel and platen by using a paper/plastic interface. We find Tas oak reacts with moisture and metal contact and creates a blue stain. Physical separation by paper stops stain. Use a wood spatula for applying putty as well; steel spatula and putty react to create a blue stain.

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From contributor R:
The blue stain is a reaction from your oak coming into contact with bare steel. The moisture in the wood reacts with the metal, causing the wood to turn blue. Are your platens covered with any type of protective barrier such as Mylar? If not, this is the most likely cause. Either way, the blue stain can be easily removed with oxalic acid (wood bleach).