Holographyforum.org / holowiki.org

Here is a hologram made by painting on the model. We shot this about 2015.

Joy's procedure for testing appropriate paints was to illuminate each colour paint by all three lasers. Using a red paint as an example for red information from the model:
1. Choose a set of red paints and paint a white card with all of them. Illuminate with red laser and choose the paints that appears brightest. This creates a subset of all the red paints.
2. Paint another white card with the subset, and illuminate with, eg, the green laser. Choose the darkest set of red painted cards; the ones with the most contrast. This creates a second subset.
3. Paint another white card with this second subset, and illuminate with the blue laser. Choose the darkest set of red painted cards, again, the ones with the most contrast.This creates a third subset.
This allows you to narrow down all the red paints to a few, or, hopefully, one.
[attachment=0]bus stop.jpg[/attachment]

As a probable correction to my earlier post, "crawling" watercolor/gouache paint (during a holographic exposure) seems more likely due to glycerin or glucose. Glycerin is known by many of us to be hygroscopic (glucose is said to be, also). One author stated that artist's watercolor paint can contain up to 20% glycerin/glucose:

https://www.watercoloraffair.com/what-is-watercolor-paint/

I only had one instance of crawling paint, and that was with artist's gouache (which is an opaque version of watercolor), so I'm thinking it was likely due to glycerin/glucose.

By the way, if anyone wants to experiment with pigments when doing RGB holograms, I've found the following to be helpful:

https://www.jerrysartarama.com/daniel-smith-watercolor-238color-dot-card

This contains 238 samples of sometimes exotic pigments. With a wet brush, you can test each one (which I've done, with surprising results under 488/532/633).

For those of us who have a Sapphire 488 (which has become a fairly common and inexpensive surplus blue laser), I've found a blue pigment which reflects an excellent blue color (similar to the appearance of a clear blue sky) when illuminated with 488nm: Cobalt Blue.

I tried a number of other blues under 488nm, and this seems best.

Also, I got my three beams together (532, 633, and 488) and looked at some random color objects with blues, and as expected, the blue color rendition was terrible. So, if someone is trying to do color holograms of "found objects" then 488 is definitely not the way to go, being close to the border of blue and green. However, if the objects are being painted by the holographer, and Cobalt Blue is an acceptable choice for blue, the outlook is promising. Also, with 488nm, I would expect less scattering noise (from whatever source) compared to 457nm.

I should note that a casein binder for the paint is preferable (link below) for my long exposures (in contrast to a gum arabic binder such as found in watercolor and gouache) since gum arabic appears to grab moisture from the air and "crawl" on the surface of the object.

https://www.jerrysartarama.com/richeson-casein-artist-colors-cobalt-blue-37-ml-05056?gclid=Cj0KCQiA-oqdBhDfARIsAO0TrGGAOPmUeWJJNIVQDu69J23lz6qqPuyOEbVj3JfWzqTJIOaUYxcwVSkaAi2cEALw_wcB