Tony DCG wrote:Thanks milan on your progress. It is great to see some DCG post and your passion is in the right place.
Thanks Tony. I am trying my best to get back on track after all that troubles with my laser(s). Now, I want to solve gelatin 'mystery'... and later will back to laser(s).
Tony DCG wrote:There are many layers to your situation and will be tough to get you on track without a level of control. Basicly meaning if this was Martha Stewart's cake baking forum (might have more followers
) and you said "well I don't have white wheat flour but rye flour, I'm not using sugar but I do have honey and the eggs I use are that from a platypus", I think it would be tough to make that cake palatable.
Exactly it is how I started: first read many 'cook-books', then started my own way. This is because, as you said, sometimes can't follow exact recipe because of missing (or wrong) ingredients.
Tony DCG wrote:Your gel mix time is OK. I'm from the school of shorter is better, mix no more than 20 minutes although you would only see suble changes if you go longer. If your gel solidifies before it hit bottom and your glass is warm then there is something really odd about your gel. This should never happen and I have tryed Bloom Strengths of 190 to 290 and never saw that problem. Make sure that the plate is laying lenght wise meaning the 20cm is vertical and the 40cm is horizonal.
Next time I will cut that plate to half. I have old stock of 20x40 cm plates bought long time ago for capacitor purpose (Tesla coil). Fortunately, I did not use all of that plate on capacitors, so now I have plenty of glass for experimenting for a while.
Tony DCG wrote:John, if your out there, have you worked with KDi? That might be a whole new ball game as it pretains to crosslinking. Since it is not as sensitive as AmDi your exposure time, fix time and post processing might be very different than AmDi. I am not sure what your exposure times are nor what laser you are using, although I think you need green to red wavelengths (right?). Whitening is also a function of no or low crosslinking.
I think something is related in differences between KDi and AmDi, but that is not strictly and directly related to sensitivity, nor post-processing.
I asked my friend chemist what he think about possibility that gelatin with AmDi mixed in retain water more easily than KDi, and whether AmDi is more hygroscopic. He said that it is possible, but not sure. If so, then next scenario is possible: What if gelation time and way of gelation (refrigerating, or keeping in humid area) differ for that two chemicals mixed in? What if rapid drying of the surface with water/gelatin/KDi mix make 'impenetrable membrane' of partially or no cross-bonded chemicals that make collagen structure (helices and triple helices)? What if layer close to the glass somehow manage to 'renaturates', while the rest close to surface not? Something about that is mentioned the gelatin manual, which Joe Farina posted relatively recently in this topic:
http://holoforum.org/forum/viewtopic.ph ... =650#p5898
Direct link:
http://www.gelatin-gmia.com/images/GMIA ... l_2012.pdf
At page 8, there is few probably most important sentences:
"Gel Strength – The formation of thermoreversible gels in water is one of gelatin’s most important properties. When an aqueous solution of gelatin with a concentration greater than approximately 0.5% is cooled to approximately 35-40°C it first increases in viscosity,
and then later forms a gel." (emphasis in bold text)
So, what I got is actually not yet a gel, but just mixture of amino acids with high viscosity, which resemble gel, but not even close. In the continuation, there is something also important:
"The rigidity or strength of the gel depends upon gelatin concentration, the intrinsic strength of the gelatin, pH, temperature, and the presence of any additives. The intrinsic strength of gelatin is a function of both structure and molecular mass."
That is maybe related of water concentration of gelatin vs. amount of dichromate. But, still that part did not yet get to the most important part, for which I am not sure how it works:
"
The first step in gelation is the formation of locally ordered regions caused by the partial random return (renaturation) of gelatin to collagen-like helices (collagen fold)."
The first step! How long it takes to all of that amino acids to form collagen-like helices? What if some of amino acids are not cross-bonded, and got lose during last hot alcohol bath? My very last plate (before flu hit me hard) come out with thin coating on glass side after last alcohol bath. Something is for sure lost from the emulsion side during dehydration. I did not paid attention to that earlier, but I bet I saw that. This doesn't bothered me as long as hologram looks okay.
Does anyone else noticed such thin (and somewhat milky) coat after last alc. bath on the glass side of the plate? And if yes, does this plate (and few other before that one) come out milky?
One sentence skipped, and then the continuation:
"Hydrophobic, hydrogen, and electrostatic bonds may be involved in the crossbonding. Since these bonds are disrupted on heating, the gel is thermoreversible.
Formation of the crossbonds is the slowest part of the process, so that under ideal conditions the strength of the gel increases with time as more crossbonds are formed. The total effect is a time-dependent increase in average molecular mass and in order (38,39)."
I think most important part is worth to 'paint' red. I think my last plates turns out milky because lack of time for such cross-bonding to happen. Note on next page of this manual that this holds for 6.67% of the gelatin!!!
What I do on my plates is initially 12% of the gelatin, BUT that percentage holds until water evaporates, mostly from the surface. As film dries, water as a 'transport' mechanism vanishes, partially cross-bonded amino acids remains, just 'sitting there' until dichromate attempting to cross-linking (and perhaps cross-bonding as well). Chemical, light and thermal hardening maybe helps dichromate to harden this part, but if just few weak bonds remains, it is also possible that such parts get lose and become lost in alcohol bath(s), and maybe later (during hot air drying) - distorting surface of the film even more (and not only at surface).
Tony DCG wrote:milan, if possible try to look at John's recipe either on his web site or in holowiki. See what is different and if you like let us know.
Also, if you need gelatin I would be happy to send you some. AmDi might not be possible but best to start somewhere. I don't mind sensing it overseas.
Best of luck to you!!
Everything is different in small quantities. From AmDi to KDi, to many other variations. Some subtle, almost unnoticed, some bit bigger. I think I will first pay attention on forming proper gel structure, and later on post-exposure fixing.
Best--
milan