Fun with dichromated gel holograms

So this is pretty much entirely based on reading the last 10 or 15 years of posts on the holography forum. I'm attempting to cite sources, but there is a lot of reinvention, so I'll probably get it wrong.

Coating

My plates are old failed holograms... mostly PFG-3C plates. I clean them off with bleach and a plastic scrubby thing, wash them off with lots of hot water, and then rinse them in distilled water and dry them vertically.

I'm using knox gelatin from the grocery store right now. Which according to people on the holography forum is about 220 bloom. I have acquired some 250 bloom photographic gelatin, but haven't tried it yet.

Right now, I'm using 12g of gelatin per 100ml of water. I've also tried 15g/100ml and 7g/100ml. This is another variable.

Pour coating

My current method for coating is to heat a plate with a hot air gun till its warm, then pour a puddle of gel into the center. Then, carefully tilt the plate around such that the puddle runs around to the corners. Surface tension will keep the puddle on the top of the plate if one is careful. Once the plate is covered, I run the puddle off one corner. I then wipe the corner off with a paper towel, and lay the plate flat on a level surface to solidify and then dry.

Its not veil coating, that would hold the plate nearly vertical, while this is level. I'm calling it "pour coating", until I find the correct term.

I copied the technique from how a friend of mine coats his wet plate collodion plates.

Mold coating

I have tried mold coating a couple of plates. They were much thinner, I' m sure they were much more reproducible.

My initial attempts with 7% gelatin were extremely dim...

I have gotten good results with 18% and 20% 250 bloom gelatin mold coated with 0.002 inch shims (scotch tape).

Meyer bar coating

Tried a couple of times. Made an epic mess, but usable results. Concentrating on mold coating right now.

Veil coating

Made an epic mess... concentrating on mold coating for now.

Sensitizing

My current method is "dip-n-dunk" or "dip-n-shoot" as described by Dave Battin on the holography forum. I put the plain gelatin plate into a solution of 1/2 percent potassium dichromate and some forma-flo wetting agent for 30 seconds. I then pluck it out, and set it on a paper towel on a level surface. Afterwords, I pick it up, wipe the back dry with another paper towel, and set it back on the level surface to finish drying.

The final result is not amazingly yellow, but it will attenuate a beam of 457nm light from 100 micro-W to 74 micro-W.

The final step is to pretty liberally hose down the work space and paper towels with a 10 percent solution of potassium metabisulfate, to reduce the hexvalent dichromate.

Exposing

My laser is a melles griot BLD-605 457nm laser. My test setup is a plain old Denisyuk hologram, at 45 degrees. My power meter claims that my beam is 100 microW/cm^2, so I'm doing a 200 second exposure, to get 20 milliJ/cm^2, but at a 45 degree angle, its really more like 14 milliJ/cm^2.

My test object is a stuffed hamster and a coin. (I have a lot of holograms of this hamster...)

Processing

I am using the chemical "fixer" approach.

5g potassium metabisulfate
3g of potassium alum
water to make 500ml

I place the plate in the "fixer" for 1 minute, and then wash it off in some distilled water. After the "fixer" its light-safe, and I turn on a white light.

The plate then goes into the swelling bath for 5 minutes. The temperature is between 23C and 34C, with the best results around 26C.

I then dry the back of the plate with a paper towel, shake off as much water as I can, and put the plate into the alcohol baths. Right now, I'm using 3 baths, 70%, 91% and 99%, two minutes in each. I've also done it with only the 91% and 99% baths. The baths are all the same temperature, from 22C to 38C.

I am controlling the temperatures using some thermocouple PID controllers off ebay controlling heating pads under the trays. I got some long skinny thermocouple probes which I submerge in the baths. I then have a thermometer in the swelling bath, so my notes tend to report both the PID temperature and the thermometer temperature.

I then dry the plate with a heat gun. It can put out significantly more heat than a hair dryer, which may be a hazard. But its what I had...

The Notes

I number my holograms by session number and then serial number. So hologram number 177.1 is the first hologram of session number 177. I have lots of pictures, but they are not especially well indexed. Also, I'm lazy and don't feel like doing all the HTML markup. So you get a pre block.

The columns:

Coat - concentration of gel to water, and method. Generally "pour", but there are a couple of mold coated.
sensitize - concentration of K dichromate to water in the sensitizing bath.
expose - number in seconds. Assume 100 uW/cm^2.
harden - concentration of K alum in the "fixer" bath.
swell(ther) - temperature of the swelling bath as observed by a thermometer.
swell(PID) - temperature the swelling bath PID was set to.
swell time - how long the hologram was in the swelling bath.
70% - time in 70% alcohol bath
91% - time in 91% alcohol bath
99% - time in 91% alcohol bath
IPAtemp - temperature the alcohol bath PID was set to. (thermometer would not fit in the tray)

I was getting basically no results (holograms 177.x) until I omitted the hardener from the "fixer". Hologram 180.x varied the hardener concentration.

In holograms 178.x, I got lots of color blobs... Which were really from too hot a swelling bath.

In holograms 180.x I started getting good images, but only when viewed from the back (pseudoscopic). The opaque white layer is between the plate and the fringes. Too much dichromate? But conflated with too hot a swelling bath.

In hologram 181.x I finally started getting nice sharp images, but very dim (I've done better with silver halide). Then as swelling and alcohol temps went up, the milkiness returned.

	coat	sensitize	expose	harden	swell(ther)	swell(PID)	swell time	70%	91%	99%	IPAtemp
Images of 176.x 

Images of 177.x 
177.1	7%pour	4.0%		155	?	C		C		1:00		--	2:00	2:00	38C PID	crystallized, washed off

Images of 178.x 
        coat    sensitize       expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
178.1	15%pour	3.0%		310	0%	33C		36C		1:00		--	2:00	2:00	38C PID
178.2	15%pour	3.0%		310	0%	27C		?		1:00		--	2:00	2:00	38C PID
178.3	15%pour	3.0%		310	0%	22C		?		1:00		--	2:00	2:00	38C PID
178.4	15%pour	3.0%		155	0%	27C		?		1:00		--	2:00	2:00	38C PID
178.5	15%pour	3.0%		472	0%	27C		?		1:00		--	2:00	2:00	38C PID

Images of 179.x 
        coat    sensitize       expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
179.1	15%pour	1.0%		310	0.1%	23C		26C		1:00		--	2:00	2:00	38C PID
179.2	15%pour	1.0%		310	0.1%	26C		30C		1:00		--	2:00	2:00	38C PID
179.3	15%pour	1.0%		310/SB	0.1%	26C		30C		1:00		--	2:00	2:00	38C PID		single beam: blocked illum
179.4	15%pour	1.0%		77/SB	0.1%	26C		30C		1:00		--	2:00	2:00	38C PID		single beam: blocked illum

From here on, plain single beam Denisyuk 100 uW/cm^2 goal is 20 mJ/cm^2, but failed to multiply by cos(45) so actually 14 mJ/cm^2

Images of 178.1 to 178.5, 179.x, 180.1 to 180.6
Images of 180.7 to 180.8
        coat    sensitize       expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
180.1	15%pour	1.0%		200	0.2%	28C		30C		1:00		--	2:00	2:00	38C PID
180.2	15%pour	1.0%		200	0.4%	28C		30C		1:00		--	2:00	2:00	38C PID
180.3	15%pour	1.0%		200	0.6%	28C		30C		1:00		--	2:00	2:00	38C PID best of 180.x
180.4	15%mold	1.0%		200	0.8%	28C		30C		1:00		--	2:00	2:00	38C PID worst, due to mold coating
180.5	15%pour	0.5%		200	0.6%	28C		30C		1:00		--	2:00	2:00	38C PID
180.6	15%pour	0.5%		100	0.6%	28C		30C		1:00		--	2:00	2:00	38C PID
180.7	15%pour	0.5%		100	0.6%	22C		25C		1:00		--	2:00	2:00	38C PID replaced 98% alcohol, it was creepy
180.8	15%mold	0.5%		100	0.6%	28C		30C		1:00		--	2:00	2:00	38C PID

Coated with 12g/100ml gelatin
dried overnight, horizontally
sensitized in 0.5 percent K dichromate, with about 10 drops of forma flo
dried from 10am to about 4pm, horizontally

Images
        coat    sensitize       expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
181.1	12%pour	0.5%		200	0.6%	21C		22C		5:00		--	2:00	2:00	22C PID  
181.2	12%pour	0.5%		200	0.6%	23C		26C		5:00		--	2:00	2:00	22C PID  increased swell bath temp
181.3	12%pour	0.5%		200	0.6%	23C		26C		5:00		--	2:00	2:00	26C PID  increased alcohol bath temp
181.4	12%pour	0.5%		200	0.6%	27C		30C		5:00		--	2:00	2:00	26C PID  increased swell bath temp
181.5	12%pour	0.5%		200	0.6%	27C		30C		5:00		--	2:00	2:00	30C PID  increased alcohol bath temp
181.6	12%pour	0.5%		200	0.6%	32C		34C		5:00		--	2:00	2:00	28C PID  increased swell bath temp, decreased alcohol bath temp

2 is very slightly brighter than 1
3 is brighter than 1,2
4 is brighter than 3, barely
5 starts getting milky and spotty.  6 is much milkier than 5.  so milkiness is a function of swelling bath,

Images
        coat   	sensitize       expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
182.1	12%pour	0.5%		200	0.6%	??		30C		5:00		2:00	2:00	2:00	30C PID  just like 181.5, only 3 baths
182.2	12%pour	0.5%		200	0.6%	??		34C		5:00		2:00	2:00	2:00	28C PID  just like 181.6, only 3 baths
182.3	12%pour	0.5%		200	0.6%	23C		27C		5:00		2:00	2:00	2:00	26C PID  just like 181.3, only 3 baths
182.4	12%pour	0.5%		200	0.6%	28C		30C		5:00		2:00	2:00	2:00	26C PID  just like 181.4, only 3 baths
182.5	12%pour	0.5%		200	0.6%	26C		28C		5:00		2:00	2:00	2:00	28C PID  movement

182.1 or 182.5 is best of 182.x  182.1 is milky  99% was replaced after 182.3
182.2 is very white, broadband caused by swelling bath too warm?
182.3 is terrible, very dim narrow green 181.4 is better
	should have been like 181.3

183.x were all done with 250 bloom photographic gelatin from the photographer's formulary

density means raw beam is the first number, the plate attenuates the beam to the second number, both in microwatts/cm^2.

Images of 183.x
        coat    density		sensitize       expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
183.1   12%myr  125->102	0.5%            200     0.0%    26C             28C             5:00            2:00    2:00    2:00    28C PID just like 182.5 only no hardener
183.2   12%myr  unmeas		0.5%            200     0.3%    26C             28C             5:00            2:00    2:00    2:00    28C PID
183.3   12%myr  unmeas		0.5%            200     0.3%    28C             32C             5:00            2:00    2:00    2:00    28C PID
183.4   12%pour unmeas		0.5%            200     0.3%    25C             28C             5:00            2:00    2:00    2:00    28C PID

183.1 is better than 183.2.  Stick with no hardener?
183.3 is the worst, exceeded the yield point, so just milky.
183.4 is the best of the set.


184.x:
two plates on monday, one meyer, one pour dried horizontally
three plates on thursday two meyer, one pour dried horizontally

Images of 184.x
        coat    density		sensitize       expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
184.1   12%myr  100->80		0.5%            200     0.3%    26C             28C             5:00            2:00    2:00    2:00    28C PID sensitized 5 days prior
184.2   12%pour 107->87		0.5%            200     0.3%    26C             28C             5:00            2:00    2:00    2:00    28C PID sensitized 5 days prior light struck
184.3   12%pour 104->20		3.0%            200     0.3%    26C             28C             5:00            2:00    2:00    2:00    40C PID sensitized 1 day prior light struck
184.4   12%myr  95->40		3.0%            200     0.3%    26C             28C             5:00            2:00    2:00    2:00    37C PID sensitized 1 day prior light struck
184.5   12%myr  111->50		3.0%            200     0.3%    26C             28C             5:00            2:00    2:00    2:00    37C PID sensitized 1 day prior light struck

The old sensitized plates were narrow bandwidth, very even color, but very dim.
184.4 was a complete failure, the coating was just too bad, and the K dichromate crystalized
184.3 was significantly brighter than 184.1 and 184.2.  very milky as well.  I suspect
the 70% IPA bath was acting like an additional swelling bath.  Faster passes in the IPA?

184.5 was a complete failure, poor coating, and crystalized.

I think the 1/2 percent K dichromate is too low.  3% is too high, and crystalizes on
meyer bar coated plates.  The best spots were the thick spots.  Meyer bar with thicker
gelatin?  (like 18%?)

185.x:
18% 250 bloom gelatin.  Coated 5 with meyer bar, mold-coated 8.  mold coating is 
more consistant, but very thin.  The spacer was 0.0018 inches (scotch tape) resulting
coating is 0.00035 inches, or 8.9 micrometers.
The meyer bar coating is 0.00080 inches, or 20.3 micrometers.

two plates sensitized in 3% K dichromate for 1 minute, then rinsed off in 1/2 % K dichromate.
	This /did/ prevent crystalization
	as per the density numbers, it still got more dichromate into the gelatin
two plates sensitized in 1/2% K dichromate for 1 minute.
senstized friday, to be exposed saturday.  about 12 hours old.

Do not heat 70% IPA, it acts as a swelling bath.
no hardener, based on 183.1 and 183.2

Images of 185.x
        coat	density	sensitize	expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
185.1	18%myr	110->81	0.5%		200	0.0%	26C		28C		5:00		2:00	2:00	2:00	28C PID 
185.2	18%myr	102->42	3.0%		200	0.0%	26C		28C		5:00		2:00	2:00	2:00	28C PID 
185.3	18%mld	91->45	3.0%		200	0.0%	26C		28C		5:00		2:00	2:00	2:00	28C PID 
185.4	18%mld	104->80	0.5%		600	0.0%	26C		28C		5:00		2:00	2:00	2:00	28C PID 


185.1 is very dim but very even.  like all of my meyer bar coated attempts sofar.
185.2 is brighter.
185.3 is significantly dimmer.  need a thicker coating, or more dichromate, or more exposure.
185.4 was pretty much a fail, insufficient dichromate and coating too thin.  There was a pattern
on the hologram like droplets of sensitizing bath drying, and increasing the dichromate concentration where the drop was.


So... new wisdom.  Don't reuse fixer, and pre-wash before fixer.  Also, MOAR dichromate.  
See thread "DCG processing, comparing apples with oranges." on the holography forum.
Investigated alcohol baths, replaced 99%, it was down to 97%.
70% bath is at same temp as swelling bath.  91% and 99% are at temp in table.

Sensitized 4 plates, 5% K dichromate for 1 minute, then quick rinse in 1/2 % K dichromate.  Slight crystalization.

Images of 186.x
        coat	density	sensitize	expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
186.1	18%myr	114->26	5.0%1m		200	0.0%	33C		35C		5:00		2:00	2:00	2:00	28C PID 
186.2	18%myr	108->27	5.0%1m		200	0.0%	26C		28C		5:00		2:00	2:00	2:00	28C PID 
186.3	18%mld	105->30	5.0%1m		200	0.0%	28C		28C		5:00		2:00	2:00	2:00	28C PID 
186.4	18%mld	110->34	5.0%1m		200	0.0%	24C		24C		5:00		2:00	2:00	2:00	28C PID 

186.1 was milkier than you can possibly imagine.
186.2 was still exceptionally milky, but had a bright broadband image.
186.3 milky and broadband
186.4 milky, the coin looks great, but very milky

Images of 187.x
        coat	density	sensitize	expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
187.1	18%mld	113->65	3.0%1m		200	0.3%	22C		24C		5:00		2:00	2:00	2:00	28C PID 
187.2	18%mld	106->44	3.0%1m		200	0.0%	24C		24C		5:00		2:00	2:00	2:00	28C PID  (mislabeled 187.1 in images)

187.1 is very dim, blotchy, and narrow band.  Too much hardener?
187.2 is less dim, blotchy and narrow band.
So, the senstizing bath, 3% vs 5% is the most significant variable between 186.x and 187.x  


Images of 188.x
        coat	density	sensitize	expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
188.1	18%mld	98->22	5.0%1m		200	0.0%	24C		24C		5:00		2:00	2:00	2:00	28C PID 
188.2	18%mld	109->23	5.0%1m		200	0.1%	24C		24C		5:00		2:00	2:00	2:00	28C PID  fixed 30 seconds
188.3	18%myr	107->24	5.0%1m		200	0.3%	24C		24C		5:00		2:00	2:00	2:00	28C PID  fixed 30 seconds


188.1 and 188.2 are nearly indistinguishable, and both excessively milky.
188.1 and 187.2 vary only in the concentration of the sensitizing bath
188.3 is wideband, and less milky than 188.1 and 188.2, but still milky.

Images of 189.x
        coat	density	sensitize	expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
189.1	20%mld	98->35	3.0%1m		200	0.0%	24C		26C		5:00		2:00	2:00	2:00	28C PID 
189.2	20%mld	97->30	3.0%3m		200	0.0%	24C		26C		5:00		2:00	2:00	2:00	28C PID 
189.3	20%mld	106->36	3.0%1m		200	0.2%	24C		26C		5:00		2:00	2:00	2:00	28C PID 
189.4	20%mld	101->36	3.0%3m		200	0.0%	29C		30C		5:00		2:00	2:00	2:00	28C PID dropped the plate

observed thickness of 20% coating is 0.00035 inches
fixed 30 seconds
189.1 is just like 187.1 only 2 degrees warmer and 20%

189.1 is best sofar.
189.2 is slightly broader band than 189.1.  
both are rather dense for denisyuk configuration, only transmitting 30 to 35% of the light.  


Images of 190.x
        coat	density	sensitize	expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
					uJ/cm^2
190.1	20%mld	unmes	3.0%1m		10900	0.0%	27C		26C		5:00		2:00	2:00	2:00	28C PID

Reprocessed 190.1 with a swelling temp of 25C.  nothing significant changed.  (expected result...)

Images of 191.x
        coat	density	sensitize	expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
					uJ/cm^2
191.1	20%mld	unmes	3.0%1m		2700	0.0%	26C		26C		5:00		2:00	2:00	2:00	28C PID
191.2	20%mld	unmes	3.0%1m		20124	0.0%	26C		26C		5:00		2:00	2:00	2:00	28C PID
191.3	20%mld	unmes	3.0%1m		20124	0.3%	26C		26C		5:00		2:00	2:00	2:00	28C PID
191.4	20%pour	unmes	3.0%1m		20124	0.3%	26C		26C		5:00		2:00	2:00	2:00	28C PID

The exposure time for 20124 uJ/cm^2 was 3600 seconds the laser mode hopped

191.1: the "base fog" (its colorful, not density) is nigh inpenerable.  I expect the density to be the same as 189.x, or about 
191.2: there is an image, behind the fog and the mode hop.  Its even bright.

The thicker emulsion was narrower band  (nice to reproduce expected observations...)
The wash and fix step was insufficient for the really thick region of 191.4

There was no course texture on the pour coated plate, so its definately a mold coating artifact.

My current hypothosis is that the "base fog" is a hologram of the emulsion itself, its too dense, and making a diffraction grating 
with the reference beam.  Sensitize some plates with lower concentration of K dichromate.  ponder 183.1  

Images of 192.x
        coat	density	sensitize	expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
					uJ/cm^2
192.1	20%mld	unmes	0.5%1m		20124	0.0%	26C		26C		5:00		2:00	2:00	2:00	28C PID
192.2	20%mld	unmes	0.5%1m		20124	0.0%	24C		26C		5:00		2:00	2:00	2:00	28C PID no prewash
192.3	20%mld	unmes	0.5%1m		30216	0.0%	24C		26C		5:00		2:00	2:00	2:00	28C PID no prewash

192.1 had even worse "base fog" thant 191.x.
192.2 and 192.3 are narrow band green, and moved or mode hopped.  It was a 1.5 hour exposure though.
192.3 is slightly better contrast than 192.2.

So the "base fog" is caused by the pre-wash.



Images of 193.x
        coat	density	sensitize	expose  harden  swell(ther)     swell(PID)      swell time      70%     91%     99%     IPAtemp
					uJ/cm^2
193.1	20%mld	unmes	3%1m		14784	0.0%	26C		26C		5:00		2:00	2:00	2:00	28C PID
193.2	20%mld	unmes	3%1m		14784	0.0%	26C		26C		5:00		2:00	2:00	2:00	28C PID
193.3	20%mld	unmes	3%1m		14784	0.0%	26C		26C		5:00		2:00	2:00	2:00	28C PID
193.4	20%mld	unmes	3%1m		16128	0.0%	26C		26C		5:00		2:00	2:00	2:00	28C PID

first "production" run of DCG holograms.  Unfortunately the subject was insufficiently stable 
in 193.1 and 193.2

193.3 was the shell, and it is the best so far.
193.4 wsa the glass dragon, and insufficiently lit.