[Alt-photo] Kallitype stain

[Tyler Boley]

I posted this at DPUG.org, but I figured the more answers the better...

I see this is an issue here, but mine is not with ongoing work and 
processing I can alter to solve. I got out a kallitype I made in 1985. 
It's been out of the light all these years. I'm seeing the yellow stain 
where the emulsion was brushed on, but neg masked off for white edge, so 
easy to see. I take it this is a clearing problem, either iron or 
silver? My question is, can I treat it in anything now to clear the stain?
Thank you,
Tyler