Different ways to black-out holograms
Published April 28, 2024
Hello! Recently I made my first succesful batch of holograms. Here they are:
Made some holograms yesterday, the best I’ve gotten far! Shoutout to Ultimate Holography pic.twitter.com/eatJqhVmJY
— Andy (@oldestasian) April 26, 2024
These holograms use the same silver halide particles as analog film photography, but with approximately 100x smaller crystal size (~10nm). Crystals of silver halide are suspended in gelatin and coated onto one side of the glass plate, this plane is then photoactive.
After a hologram is shot, it's good practice to black out the gelatin side of the hologram as it both protects them and makes them easier to see. After shooting my holograms, I wanted to compare a couple ways to do it and document my results.
Black Tape
The funny thing about black tape (duct/gaffer) is that usually the sticky side is white. I found electrical tape to have a black sticky side, but wasn't able to find any that was wide enough to cover my glass plates in one piece. I tried abutting them edge-to-edge instead.
Tape abutment works ok for blacking out holograms
You'll notice this kinda works, but the gaps are clearly visible. Even for perfect alignment, there will be a noticeable thin line. There's also some bubbles — these are easy enough to get out by scratching at the tape so it flattens out, but sometimes there are bigger bubbles which do not come out easily. If done carefully it won't look too bad.
Air bubbles trapped in the tape backing. Remember manually putting on phone screens like this?
Black Tape, Overlap
If the tape is instead placed over the next piece, this line only gets worse. I cannot recommend this method cause it really sucks.
Overlapping tape backing
Paint
Lastly, I tried a matte black spray paint. One nice thing about this is that we don't really care about the finish on the back side so you can spray a pretty thick single coat. Here is a sheet I taped and spray-painted for comparison.
Holograph plate taped (left) and spray painted (right)
Difference in black effectiveness from the visible side
In the circle above you can see the difference in contrast between tape (bottom) and paint (top). I would say the spray paint is a tad darker, and can go on more evenly. This is definitely the nicest method.
Anyway, now you know!