Mold Coating

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Mold coating is the process where you use spacers between two pieces of glass, one with a release agent, in order to get an even coating thickness. Depending on the exact chemistry desired a coating thickness is set by the spacers. A place to start is 7um. Swollen unhardened gelatin can contract on hardening by a factor of 8, but partially hardened stuff can be less than half this.

  1. Take two identical pieces of glass. One with tape on two opposing edges. Different tape thicknesses will yield different final emulsion thicknesses.
  2. Treat the piece of glass without the tape with Rain-X to prevent sticking.
  3. Place a small puddle of emulsion in the center of the plate with tape on it. Make sure the emulsion does not have any air bubbles in it. With practice a known about of emulsion can be used that covers the plate but with minimal excess and overflow. #Then gently lay the piece of glass without tape and with the Rain-X (Rain-X side facing the emulsion) on top of the puddled glass as flatly as possbile. You will see the puddle of emulsion expand though th entire plate.
  4. Place 4 black paper clamps, two on each side right over the tape.
  5. After the gelatin has dried, minimally 3 or 4 hours, gently pull them apart. A very flat surface is left behind.

Tips

  • I would add that air bubbles in the gelatin can be removed using the edge of piece of adsorbing paper. I found bubble formation is a quite common problem when making plates. - Cristiano

Tips from Dave Battin

The glass I use for my mold is 1/4" mirror (back silver), while I won't call this glass optically flat, it is of optical quality.

The Rain-x is the key, I put a couple drops on the mold, then buff it in, heat the mold and film plate, and meter out the emulsion. To see the emulsion do a little dance on the rain-x is really amazing!

I have a "two suction cup" handle that I use to hold my plate and slowly drop/ hinge the plate along the taped edge of the mold. I then place six larger paper clamps around the perimeter

My plate size is 5"x 15" and i can get 3 nice 4x5s per mold , If metered carefully (absolutely leveled mold) ,only a few drips will come off the mold ends ………….

As soon as the gel sets (a few mins) I move the still slightly warm plate and mold, on to a frozen piece of granite, where it rapidly cools down. Buy the way the granite can work both ways, for both cooling, and heating! I purchased these as granite tiles a the local Depot (12"x12"), and cut them up ........

The tape I used is plain Scotch Tape and is .0025” or @ 63 microns thick.

And to my surprise the film thickness came in @ .0004” or @ 10 Microns.

The gelatin was Knoxx brand at a 15 grams /110 ml DI water, poured @ 70+degrees C.