Rust spots on kallitypes

[tnp651]

Every once in awhile I'll get a spot like this when I coat for a kallitype. The sensitizer looks perfectly clear, but as soon as I spread it, I get a spot. There's no way to remove it and it ruins the print. Does anyone know what causes it and how to prevent it?

 

[ced]

What is used to apply the coating to the paper brush, rod or foam? ( a metal ferrule could be a culprit ).
Any treatment to the paper before the coating? If so, does it come into contact with metal etc.?

 

[tnp651]

Thanks for responding. I'm rod coating. The paper is uncoated Arches Platine (no fumed silica, for instance). The paper is kept in its original plastic bag until time for coating. The spots appear as the coating is pulled across, as though there was something in the paper. The bottle of ferric oxalate is about 9 months old, and about 1/4 full. FWIW I used a second, full bottle (bought at the same time) and the one print I made from it was perfect.
Tom

 

[ced]

Could it be crystal/crystals coming out of the bottle?
Try filtering, then rinse the bottle out with H2O Dist.

 

[tnp651]

I'll try it.

 

[wyofilm]

I don't know how large your paper is, but that splotch looks pretty large. As suggested above, looks like a crystallized material. Is that where you first applied your coating liquid? It looks like the material was was pushed in two directions, across and up.

 

[tnp651]

I coated a 9.5x12.5 inch portion of an 11x15" sheet. The splotch was about 1/8" in size and smeared out to about 3/8" in length as I tried to work it into the rest of the coating. The splotch appeared on my first pass of the rod, exactly where you see it. Normally I give 2-3 passes with the rod, then gently brush up/down and left/right to get an even coating. There was enough excess coating at the start to have diluted the spot with the brush, but it was firmly set in the paper.

I've learned to carefully examine my beaker of solution before pouring it on, and there were no crystals in the liquid.

 

[ced]

Also how clean do you keep the rod?? (only trying to figure the cause...)

 

[tnp651]

Clean enough, I guess. It's homemade, hard plastic, and I rinse it off immediately after coating. BTW I filtered the old FeOx and didn't find any crystals. My second kallitype with the other bottle was fine. Maybe the half-empty bottle is going bad... Just a thought.
Tom