Novel glass-coating methods?

Dichromated Gelatin.
pluto
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Joined: Fri Feb 05, 2016 2:06 am

Novel glass-coating methods?

Post by pluto » Thu Mar 01, 2018 2:21 pm

Creating this thread by "popular demand" :lol:

In an unrelated thread, forum member Zeta asked if glass could be uniformly coated with gelatin using a silkscreen process.

I think it would be good to brainstorm some possible ways to apply a uniform coating of gelatin to glass consistently and easily.

Silkscreening is a great candidate, but what about other methods?

- What if you spray-coated very thin layers of thin gelatin onto glass? Once each layer dries, the thickness or thinness of the original gelatin mixture shouldn't matter right? Basically, can we spraypaint gelatin onto glass and have a good surface finish?

- What about hydrocoating? Demonstration here: https://www.youtube.com/watch?v=NlwZ9pUQlro

Well, obviously water wouldn't work as the liquid, but something that gelatin is insoluble in. Seems messy but could be worth it for large plates.

- What if you had a frozen block of gelatin and a really sharp blade -- would it be possible to shave off very thin films? Could those films be pressed onto glass cleanly?

Share your ideas, even if they're half-baked :)

Steven
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Joined: Sat Jan 31, 2015 8:14 pm
Location: Cornwall, UK

Re: Novel glass-coating methods?

Post by Steven » Thu Mar 01, 2018 4:30 pm

What coating method do you use Pluto, and what size of plates are you making?
What are your failure modes?

I did briefly try veil coating without much success. Like much of DCG, I found it difficult to get consistent results.
I find that mould coating (casting), gives me consistent results.
However, bubbles in the resultant coating can be a problem.
At the moment I'm getting about a 50%-75% rejection rate due to bubbles.
I haven't had any recent failures cause by the coating peeling off when parting the plates, I seem to have that sorted.

My plates are 5" x 18" using 2mm picture framing glass.
I use a piece of 6mm glass of the same size as a supporting backing plate, this prevents the 2mm glass from bending.
The mould is 5" x 17.5" x 6mm, so this leaves two 0.25" uncoated areas at each end of the plate.
Before I started using a 6mm supporting backing plate, I had some plates that had coatings that were thicker in the centre.
The 5" x 18" plates are cut in half, giving me two plates of 5" x 9" to work with. The extra length means that the edge
of the plate does not cast a shadow on the work piece. The final hologram is cut down to 5" x 7" and the "top" two inches
are removed before processing. In fact, I use the top 2" cut off as a test run through the processing work flow.

I suspect that my method of mould coating is quite labour intensive compared with other methods, but
it does give consistent results, even if the bubbles are not in exactly the same place.

I did try an experiment, clamping the plate and mould together and drawing the gelatin between the plates
using a partial vacuum, but that didn't work.

I did think of another (modified) casting method, but I have not tried it yet.
That is to use my current method, but allowing the gelatin to set on the plate and then apply the mould.
I would then reheat the mould and plate to turn the gelatin to a liquid state again, so it spreads out evenly
without bubbles.

BTW, the bubbles I'm getting are not in the gelatin solution, but are a result of the mould contacting the gelatin solution unevenly.

Steven
Success through failure - the amateur DCG holographer's path to enlightenment.

pluto
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Joined: Fri Feb 05, 2016 2:06 am

Re: Novel glass-coating methods?

Post by pluto » Thu Mar 01, 2018 5:05 pm

Steven wrote:What coating method do you use Pluto, and what size of plates are you making?
What are your failure modes?
I've only ever veil coated without spinning, plate sizes vary from 3x4" to 5x7".

As for failure modes, the major ones are:

- Emulsion dripping down the wrong side of the glass
- Bubbles in the emulsion

Annoying parts of the process:

- The insane amount of excess emulsion required to coat plates, as much of it spills off in to the drip tray
- Having to constantly pour emulsion from drip tray back into squeeze bottle

Getting glass very clean and free of dust is tough without constantly replenishing your supply of distilled water or other solvent. I clean glass with Comet powder (amazing for cleaning things very well) then rinse with tap water. When I place the glass into a washing container, the liquid eventually gets too contaminated with minerals from tap water.

IDEA: Steam cleaner for glass plates! Once you get them passing the water-break test, stick them in a container where steam condenses and washes away the minerals, then lets them dry.

As for mold coating... it seems like a good method but very tedious. Veil coating is tedious too, and I'm not even doing the spinning or taping off edges to prevent spillover.

Mold coating a large piece of glass then cutting it up sounds a little bit better. I like how it doesn't waste so much emulsion though.

I'm too lazy for anything that seems involved or uncertain :P If I could invest $500 in some equipment or even a machine to reliable coat plates, it would be well worth it.

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admin_jsfisher
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Re: Novel glass-coating methods?

Post by admin_jsfisher » Thu Mar 01, 2018 5:46 pm

Have you tried using a Meyer bar?

pluto
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Re: Novel glass-coating methods?

Post by pluto » Thu Mar 01, 2018 9:16 pm

admin_jsfisher wrote:Have you tried using a Meyer bar?
I tried to find one for sale online some time ago, but I had trouble finding any. The fact that "mayer bars" are also known as meyer bars, meyer rods, meter bars, meter rods, metering rods, equalizer bars, doctor rods, etc. doesn't help.

I'll have another look now that you mention it though.

jrburns47
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Location: Oyster Bay, NY

Re: Novel glass-coating methods? Doctor blade coating

Post by jrburns47 » Fri Mar 02, 2018 12:29 am


Steven
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Joined: Sat Jan 31, 2015 8:14 pm
Location: Cornwall, UK

Re: Novel glass-coating methods?

Post by Steven » Fri Mar 02, 2018 6:41 am

"- Emulsion dripping down the wrong side of the glass
- Bubbles in the emulsion

Annoying parts of the process:

- The insane amount of excess emulsion required to coat plates, as much of it spills off in to the drip tray
- Having to constantly pour emulsion from drip tray back into squeeze bottle"

That is why I use dip and shoot.

I can coat my plates under normal lighting conditions, I don't worry about gelatin getting on the back of the plate,
if it does, I can clean it off under normal lighting. There is very little chemical waste and I don't need to worry about
getting emulsion back in a bottle. I only sensitize plates that have a good defect free coating.
AmDi consumption is very low.

I find that coating plates is the most difficult part of DCG, and is best done when you can see exactly what you are doing.
Everything else in DCG becomes a breeze, once you have done a few holograms.

The downside of dip and shoot, is that the surface of the emulsion is likely to pick up dust particles while it's drying,
but I expect the same problem using the veil coating method.

"Getting glass very clean and free of dust is tough without constantly replenishing your supply of distilled water or other solvent. I clean glass with Comet powder (amazing for cleaning things very well) then rinse with tap water. When I place the glass into a washing container, the liquid eventually gets too contaminated with minerals from tap water."

I stopped worrying about using tap water for cleaning the glass. Now I only use DI water for the gelatin coating and the last
water bath just before it goes into the first IPA bath.

My glass preparation method:

Cut glass to size and remove all sharp edges using a carborundum stone under running water.
Wash glass using using none scratch pad and washing up liquid. Dry and store the glass for when required.

Inspect glass and determine which surface is to be coated, if there is a scratch on the glass, that is the side that I will coat.
Using a carborundum stone and under running water, I put a small chamfer on the surface on one corner of the glass.
This helps to identify the surface I intend to coat during the cleaning process, right up to the actual coating.

Rinse glass under tap water and place in photographic tray face down.
I mix a very strong solution of Sodium Hydroxide and tap water, I also add a good squeeze of washing up liquid - take care
as the reaction of Sodium Hydroxide in water is exothermic. I only need about 60ml of this solution to clean two pieces
of glass, each 5" x 18". I use a none scratch scouring pad (no sponge) to clean the back of the plates, I then turn the plates
face up and clean that surface for a couple of minutes. I leave the plates like that for 20 mins or so before scrubbing again.
I do not flip the plates over to clean the backs, I just keep scrubbing the surface that I'm going to coat.
I do this for a few hours, scrub for a few minutes, leave for 20 minutes.

I thoroughly wash off all the Sodium Hydroxide under running tap water before placing them in Hydrochloric acid
face up (identified by the chamfer on the corner of the plate). The last time I checked the SG of the acid
it was about 9% HCl, so will need to add more water. I think that most of those using HCl to clean glass are using between
2% and 5% HCl.

After the glass plates have been in the acid for a few hours, I remove them from the acid bath (stored in the garage) and rinse
with a hose pipe before taking them into the house. I then rinse thoroughly under running tap water wearing surgical gloves
while rubbing the glass surface using my fingers. I used to rinse the glass after this with DI water, but lately, I haven't bothered.
I then dry the glass with tissues.

Steven.
Success through failure - the amateur DCG holographer's path to enlightenment.

Steven
Posts: 34
Joined: Sat Jan 31, 2015 8:14 pm
Location: Cornwall, UK

Re: Novel glass-coating methods?

Post by Steven » Fri Mar 02, 2018 7:36 am

pluto wrote:
admin_jsfisher wrote:Have you tried using a Meyer bar?
I tried to find one for sale online some time ago, but I had trouble finding any. The fact that "mayer bars" are also known as meyer bars, meyer rods, meter bars, meter rods, metering rods, equalizer bars, doctor rods, etc. doesn't help.

I'll have another look now that you mention it though.
It does look quick and easy:

https://www.youtube.com/watch?v=Y-iDF1pKJJA

A home made project perhaps:
http://cheminstruments.com/media/wysiwy ... -chart.pdf

Ready made:
http://www.ascottshop.com/uk/acatalog/F ... cator.html

Steven.
Success through failure - the amateur DCG holographer's path to enlightenment.

pluto
Posts: 95
Joined: Fri Feb 05, 2016 2:06 am

Re: Novel glass-coating methods?

Post by pluto » Fri Mar 02, 2018 12:56 pm

Steven wrote:
pluto wrote:
admin_jsfisher wrote:Have you tried using a Meyer bar?
I tried to find one for sale online some time ago, but I had trouble finding any. The fact that "mayer bars" are also known as meyer bars, meyer rods, meter bars, meter rods, metering rods, equalizer bars, doctor rods, etc. doesn't help.

I'll have another look now that you mention it though.
It does look quick and easy:

https://www.youtube.com/watch?v=Y-iDF1pKJJA

A home made project perhaps:
http://cheminstruments.com/media/wysiwy ... -chart.pdf

Ready made:
http://www.ascottshop.com/uk/acatalog/F ... cator.html

Steven.
True, seems like something you could become quite quick and proficient at.

I think I'm going to buy one of their "DRAW DOWN WIRE BAR COATERS", but which thickness should I be aiming for? Since each rod is only designed to produce a precise thickness, I'd really like to get it right the first time :)

Steven
Posts: 34
Joined: Sat Jan 31, 2015 8:14 pm
Location: Cornwall, UK

Re: Novel glass-coating methods?

Post by Steven » Fri Mar 02, 2018 2:36 pm

"I think I'm going to buy one of their "DRAW DOWN WIRE BAR COATERS", but which thickness should I be aiming for? "

From the link:

"Spiral bar coaters are used to apply a film on thin materials such as sheets or plastic, so that the hiding power
of the coating can be measured. This range of products works on flexible substrates, and with motorized film applicators."

I don't know what the difference is between those bars and the ones used by hand, or even if they are suitable for use on an inflexible glass substrate.

Regarding thickness, the thickness of the coating given is in the wet state, so you will have to do a couple of calculations.

I'm using Scotch tape spacers for my mould coating and I have estimated the thickness by stacking ten layers of tape
on top of each other and measuring the thickness with a micrometer, then dividing by ten. The tape comes out
at about 56µm for a single layer.

I'm using a gelatin solution of about 16.6% (14g gelatin + 70ml H2O).
Assuming that all the water is gone when the coating is fully dry, that should result in a coating about 9.3µm thick.

Your coating thickness will depend upon the gelatin to water ratio and the wet coating thickness,
I also believe that the speed of the bar being dragged across the surface is another variable.

The temperature of the plate will need to be warm enough to allow the gelatin to "join up" and form a homogeneous
single layer. The glass will need to be on a level surface.

Steven.
Success through failure - the amateur DCG holographer's path to enlightenment.

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