Letter 24034

Tin coat yellowing in steam [Connecticut] 

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Dear knowledgeable finishers:

I wonder what causes tin coating over brass to yellow after exposure to water steam for few hours. Different parts show various degree of yellowing. Does anyone have any means to prevent such yellowing? In the form of post-treatment, or polarisation pulse(s)?

Thanks,

Alexander Scheglov
- New Milford, CT, USA

Plated tin coatings do tend to yellow as they age. This is an oxidation of the surface. Steam speeds up the process. It can be reduced by treating the tin coating with a post dip after plating to passivate the surface.

Gene Packman
- Syosset, NY

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