The subject of what to do instead of index matching film to glass comes up periodically so it was again time to write up a tutorial.
The steps outlined here are based on using Kapco OPCLR along with 2mm and 3mm glass. Bernadette at Laser Reflections uses Flexmount which is a more expensive material. I started laminating film to glass more than a year ago based on information from Bernadette.
If you have a powered adjustable laminator, by all means use that although these instructions involve the use of a Brayer roller. A moderate amount of heat would improve the quality of the lamination and may be worth the expense to some. Items needed before starting:
o 6-8” brayer roller. Use a hard rubber roller, not the soft rubber more frequently found in art stores.
o Kapco OPCLR or similar clear laminating material. What you are looking for is a material that has a binding adhesive and a cover sheet on both sides. It should also be optically clear and non-birefringent. If you aren’t sure, obtain a sample first.
o 2-3mm thick window glass. If you can afford optically clear glass, use it. Otherwise plain window float glass is good enough.
o Friction pad. You can make a pad out of the material sold in hardware stores and used as shelf liners. This pad will keep the glass from sliding as you roll out the laminate and film.
o Holographic film. You aren’t going far without this.
o Scissors or a sharp xacto type cutter. Don’t bother attempting to use a paper cutter as the adhesive in the laminate will gum up the cutter. If you have the equipment for cutting matt-board you may be able to use that if you’re picky about perfectly straight cuts.
o Metal ruler. You’ll be using this to both measure out the sheets before cutting and also as a cutting guide.
o Window cleaner. Windex is fine for this although I’ve sometimes wondered if bleach might be better simply because of the subbing action it might provide.
o Masking tape. I use blue painters tape but you may need to choose another color depending on the color of your laser (mine’s red). Choose something that absorbs light from your laser.
Set out all the materials, clean your work table and put down the friction pad. This will be where you do all the rolling.
Measure and cut a sheet of the laminate slightly larger than the glass you’ll be using. Why larger? I’ve found it much easier to align the laminate on the glass if you’ve got some extra to work with. You’ll also find that starting the rolling process is much easier if you overlap the laminate on the glass.
Clean the glass thoroughly on one side (don’t bother with other side yet). Now clean it again. Did I mention that you should clean the glass? Make sure that there aren’t any specs of dust on the surface. If there’s anything on the glass you’ll end up sealing it in and either have to live with the result or pull the laminate off and start over. One or two small specs of dust may actually not be a deal breaker since small imperfections won’t ruin a transmission hologram intended to be used as a master for image plane copies.
If you can, purchase a HEPA air filter and just keep it running in your lab. It’s worth it in the long run to keep the dust levels down. I know of one major holographer who kept his fan running all the time and had no draft enclosure around his table. He never had a problem with air currents affecting his work. Your mileage may vary but give it a shot.
Now that the glass is clean, lay it clean side up on the friction pad.
Take the laminate and remove the top inch of protective layer from one side. You don’t want to remove the entire sheet because you need to be able to handle it up to the point where it’s rolled onto the glass with the brayer. I just use my thumbnail and slip it under the protective sheet. Sometimes I do need to snip off just the tip of one corner but most of the time I can slip my nail under the sheet with a few tries as long as I haven’t cut my nails too short.
Now very carefully align the exposed end with the edge of the glass. Let the laminate just touch the edge so that it sticks and you can support the rest with one hand. Press down on about ¼” worth along the end with your finger. This just gets things started.
Take the roller and put it on the laminate where you pressed it down with your finger. At this point you’ll have a bit of the laminate sticking to the glass, some of the protective sheet sticking away from you, the rest of the laminate sticking up in the air and your roller poised for action.
Here’s the part that really takes practice. Grab the protective sheet and pull it up and toward you over the roller so that most of the laminate is exposed. Do not let it touch the glass.
Now you can carefully start rolling. As you push the brayer forward apply a fair amount of pressure and lead the roller with the laminate so that it sits halfway between the glass and the roller. You don’t want the roller to stretch the laminate and you also don’t want the laminate touching the glass unless the roller is pushing it down.
At some point in this process (depending on the size of laminate you’re using) you’ll run out of laminate and have to pull off more of the protective layer. Be very careful doing this so that you don’t pull too hard against the roller and you don’t let the laminate drop onto the glass.
Once you’ve got the laminate rolled out, hold it up to the light to see how you did. If all went well you should have a piece of glass covered with plastic and no bubbles or dust showing.
The next step is much easier.
Take your film (do this under safelight conditions) out and while holding it in one hand, remove the last protective layer from the laminate.
Carefully place one edge of the film down on the laminate (emulsion side up). I really do mean edge. As soon as it touches, you’ll probably have to pull hard to get it back off.
Now take the brayer and press down on the end of the film with the roller and simply begin rolling across the film to stick it to the glass. Use the same method mentioned above where you keep the film halfway between the roller and laminate so that minimal pressure is needed to advance the roller.
Now look through your plate at your safelight. Any bubbles or dust? If not, you’re good to go. If there are one or two bubbles or specs of dust you may have to reserver this plate for transmission masters rather than reflection copies.
You can now use the Xacto knife to clean up the edges. Run the blade along the edge of the holographic film to cut the excess laminate. Once you’ve done all four edges you should be able to simply pull the excess off the plate.
To finish your plate take the masking tape and tape off the edges of the film and glass. If you’ve used glass that is slightly larger than your film you should be able to get away with one piece of tape for each edge of your “plate.”
Note that if you plan on pre-soaking your plate, you should do it before taping the edges and put the masking tape on after the plate has dried completely.
For best results, wait 12 hours after making your plate before you put it into any liquids. That gives the adhesive more time to bond to the film and glass. During this waiting time you should tape down the ends if you’re using roll film. Slavich film has a pretty strong tendency to curl and can cause the last ½” to debond unless it’s taped down while the adhesive cures.
If you see really bad bubbles after putting the laminate down, you can usually peel it off and start over with a new sheet. If you see bad bubbles after putting the film down, you’ll have no choice but to peel all of it off and throw the film away.