Re: a versatile surfactant that kills bubbles

Ryuji wrote:

> Anionic surfactants of sulfonate types (e.g. Triton X-200)
> seems to be very effective in improving spread of emulsion, but I
> found these way too bubbly for brush coating.

If I may ask, why are you brush-coating gelatin emulsions? For a specific
look? I'm curious because I've been coating gelatin and collodion
emulsions on glass, mylar, and paper for several decades and wouldn't even
consider brushing it on.

Lacking a proper traveling slot-and-striker coater, one can obtain good
results using a technique similar to that used for wet collodion: pour warm
emulsion on a warm substrate (mylar and paper should be firmly held to a
warm glass plate for flatness and heat retention), tilt the plate in all
directions to cover the whole area, set it down strictly level to allow the
coating to even out, after 5-10 minutes move it to a chilled environment to
set the gel, then dry it in forced air.

Decent results can also be produced with a coating rod wrapped with very
fine wire. (The original sources said to wrap in a spiral. I found that
putting a number of discrete "rings" of wire on the rod worked much better.)

With either method, when coating paper it is often a help to moisten the
paper so the emulsion doesn't soak in so deeply. (I almost always coat
commercial baryta paper, so there is no need for this.) When coating
mylar, it is much easier to start with a product like DuPont Cronar, which
has a hydrophilic coating, than to try subbing it yourself.

Speaking of proper traveling slot-and-striker coaters, one of the old
sources -- I think it was Burbank -- showed how to build one out of wood
simply enough that any alt-process practitioner should be able to make it
or easily have it made. James Browning, of Digital Mask in New Hampshire,
published plans for a much more sophisticated system, which is legitimately
capable of coating mylar film about as well as the Big Boys do it (albeit
in much smaller quantities). Jim has described his coating machine on the
Web, and plans are available on CD directly from him.

Best regards,

etienne
Received on Sun Jan 16 15:15:17 2005