How to use the new tissue -- Revised I, As far as we know now. Options

[richsul]

We're learning as we go, but this is how I think we need to handle the new tissue. Be aware that this is a moving target.

Sensitizing

Sensitizing bath at @ 55 to 65 Deg F. Can even be colder.

We store drugstore 70% isopropyl alcohol in our freezer and use it 50:50 or 40:60 in the mix with water. Right out of the freezer. This brings the temperature down.

Note that the tissue will seem leathery but it will have absorbed the dichromate.

Soak for @ 2minutes -- 2 1/2 is ok.

Old Way:

Remove and lay the back on a sheet or two of newsprint and squeegee the gelatin surface with a >clean< window squeegee. If the tissue has been sensitized in a cold bath it should take a fairly firm stroke. A quick spray with iso alcohol and maybe some photoflow immediately prior to squeegeeing may help.

Do not turn over and do the back side.

Better way from a McGraw Tech Sheet

Squeegee to a degreased plastic sheet, strip and hang to dry.

Drying

Erika Schneider did not squeegee and just hung hers to dry with no problems. I find this hard to believe but happy to hear it.

Hang to dry. My 1905 manual says not to hang it near the cesspit as the fumes may fog it

When surface is dry to the touch, remove and use immediately or freeze. We use inexpensive 4 inch irrigation plastic pipe cut to appropriate length and store curled up in the tube with 2 end caps. Glue on one end and mark the other. In the US the tube is about $7.95 for a 10 foot length and the caps are $1.79 each.

Exposing

Expose in the normal manner.

Mating to the copper

Cool water at @ 60-65 Deg F.

NO ALCOHOL IN THE WATER!

@ 15 secs or until the corners are almost laying flat.

Carry the pair to the squeege board with as much water as you can and firmly squeegee to the copper. A firm strong stroke and the water help "flood out" air bells.

The copper should be polished and bathed in a salt (NaCl) and acetic acid bath.This produces a mild hydrochloric acid that cleans the copper oxide. The oxide can tan the gelatin. The copper should be use immediately after the acid strip as oxides can build almost instantly.

Wait 15 minute -- Lother was successful developing immediately. I recommend some time as it is on your side.

If the tissue backing is not stripping quickly enough, you have not soaked long enough. Gelatin absorbs water better when the water is cold. Hot water will just slime the surface and close the molecular pores, this is why we swell gelatin first before melting. If you dump gelatin into hot water you get a slimy mess and it takes forever to melt, if it melts at all.

Developing in hot water melts the gelatin and water mixture, dry gelatin won't melt. The reason alcohol was used to wet the paper was so that heat could transfer. Paper is a good insulator and hard sized paper that was used as a backing does not wet readily but alcohol does lower the surface tension allow water to pass and then the heat to transfer.

Longer mate times allow more water to migrate up into the drier gelatin creating more of a capillary "vacuum" which creates more adherance to the copper.

Developing

Develop in the normal manner. Tests appear to indicate a longer development time.

Etch

Etch in the normal manner.

Feedback

If you learn anything let me know and I will post it. Post in the normal forum and I'll update here. This is a read only forum.