HOW are they made?
glass
It all begins with an sheet of glass. Glass sheets are carefully cleaned with strong base and detergent, scrubbing to remove any contaminant and leave a pristine surface for coating. The sheets are rinsed with deionized water and dried in a warm air oven.
Laser Optics
Not any laser will work for holography. It must be a scientific grade unit emitting a single wavelength.
During an exposure, the plate and object must remain absolutely motionless. Even slight thermal expansion of the object or vibration from walking nearby will spoil the image. The optical table is mounted on air cushions to isolate it from any surface vibration.
A special table is used to clamp down optics in the beam path. A series of mirrors guide the beam and special optical components are used to control polarization and split the beam. The beam is focused through a tiny pinhole in a spatial filter to produce a smooth light field.
The optics table is housed in a special enclosure, and the laser room is shielded from the rest of the laboratory environment to shield from air drafts and temperature gradients.
The final product
After all these steps, the hologram is finally ready.
Holograms are best viewed with light coming from a single point, such as a flashlight, spotlight, or the sun.
EMULSION
The emulsion is what makes the hologram, the photosensitive material. My holograms are created in dichromated gelatin, which is a material sensitive to green and blue light.
Gelatin powder is combined with distilled water and warmed to melt the gelatin. The liquid is stirred on a magnetic heat/stir plate. Once the gelatin is fully liquid, a measured amount of ammonium dichromate is added. After this point, the mixture is photosensitive and must be handled in darkness or red darkroom lighting.
The gelatin is filtered to remove any suspended particles, then returned to the heating plate to await coating.
Exposure
The optical table is set, the plates are ready, it is time to perform the exposure!
Before placement of the plate, the beam is blocked with a shutter. The plate is then placed in the desired position, and allowed to rest for several minutes to equilibrate with the surroundings. After equilibration, the exposure is made. A controller is used to operate the shutter automatically, allowing controlled settling and exposure times.
For some holograms, multiple shorter exposures are performed on one plate. Just like in photography, the final hologram contains all the exposures in one image.
LAMINATION
After development, the emulsion is delicate and easily damaged. In addition, the finished emulsion is sensitive to moisture, including atmospheric humidity. To preserve the hologram image, a thick sheet of fresh glass is cut to serve as a cap. Durable UV epoxy is used to seal the hologram beneath the glass.
COATING
The plates are coated with emulsion using a thick sheet of glass as a mold to create a uniform layer.
Strips of tape are applied to each side of the clean glass plate. A portion of warm emulsion is placed on the plate, and a second piece of glass, coated with water repellant, is lowered on top. The result is a thin trapped layer of emulsion, the thickness of the tape.
After cooling, the plates are separated. The repellant plate does not stick to the gelled emulsion, and peels away cleanly. After drying in a warm air circulator, the plates are allowed to cool and are ready to be cut into smaller pieces.
DEVELOPMENT
The plate is rinsed to remove the chemicals. The emulsion begins to swell as it absorbs water. The initial rinse is collected to be treated before disposal. Rinsing continues with agitation under running water for several minutes.
After rinsing, the plate is moved through a series of isopropyl alcohol baths, finishing in a warm bath.
The plate is then removed, rinsed with fresh alcohol, and dried carefully with a heat gun.
Grinding
After lamination, the edges are still as sharp as broken glass. To produce a finished product, the hologram is ground with a series of diamond discs to smooth the edges. A rounded edge is produced, and a final polish applied with diamond paste and a buffing wheel. The finished hologram has clear edges and feels great in the hand.