Victor, if you plan to seal the cyanotype to protect it physically, mind that it needs a small supply of oxygen to regenerate from the damaging effect (fading) due UV exposure, or has to be perfectly protected from UV light. I mean the seal has to be permeable to air, or perfectly protect the image from UV light. If not, you MAY loose the image (or experience unacceptable levels of fading) in the long term, due cumulative effect of UV light to the image - if it wasn't given the chance to repair itself... Framed cyanotypes normally have fading / regeneration cycles; some fading occurs when the image is subjected to UV light, then the image partly regenerates in the dark by the action of oxygen trapped inside the frame.