emulsion on glass: wetting agent or not...

Ian Grant · May 6, 2008

No in the UK % proof is very different to % alcohol.

% Proof comes from the British Navy. To test Rum and ensure a consistent measurably strength and it hadn't been watered down to much they used the Proof test. If gunpowder is soaked with Rum it will not ignite & burn if the alcohol/water mixture is below 100% proof. From memory that's approx 57% alcohol

The US proof system is based on 100% Proof being 50% alcohol.

Ian

gandolfi · May 6, 2008

Ian Grant said:
No in the UK % proof is very different to % alcohol.

% Proof comes from the British Navy. To test Rum and ensure a consistent measurably strength and it hadn't been watered down to much they used the Proof test. If gunpowder is soaked with Rum it will not ignite & burn if the alcohol/water mixture is below 100% proof. From memory that's approx 57% alcohol

The US proof system is based on 100% Proof being 50% alcohol.

Ian

thanks for that explanation! Now it all makes sense....

dwross · May 6, 2008

I just read all the posts about alcohol. You learn the darnedest things on APUG! And get the darnedest ideas. Since it is my practice (more times than not) to apply vodka to the photographer at the end of the day, I think it makes perfect sense to apply vodka to the photography. I'm going to see if Absolut can be used in place of some the water and surfactant. I'll let you know .

In the meantime, I use an atomizer/mister spray bottle to spritz the emulsion with Everclear (actually 'Clear Spring' in Oregon) when a need arises. A regular spray bottle has too coarse an application. I use the little bottles that lens cleaner comes in - the kind that opticians give away with eyeglasses. (Make sure you clean the bottle well first).

And, Kirk: magnesium carbonate and don't you dare laugh.

d

Photo Engineer · May 6, 2008

Either Photo Flo or Everclear will work. If you use Photo Flo 200 use 3x the amount of Photo Flo 600, or thereabouts. Everclear was used years ago by early plate coaters as the surfactant.

The key is that chrome alum creates a bond with chrome - gelatin - silicate glass which helps keep the coating on the glass. A simple prebath of 10% chrome alum for 5 min, then a 5 min wash will work.

Hope this helps.

PE

gandolfi · May 6, 2008

Photo Engineer said:
Either Photo Flo or Everclear will work. If you use Photo Flo 200 use 3x the amount of Photo Flo 600, or thereabouts. Everclear was used years ago by early plate coaters as the surfactant.

The key is that chrome alum creates a bond with chrome - gelatin - silicate glass which helps keep the coating on the glass. A simple prebath of 10% chrome alum for 5 min, then a 5 min wash will work.

Hope this helps.

PE

it will - apart from the fact, that I (proberly) can't get the crome....
(then it's not a fact, is it?):rolleyes:

but I'll try and see whether the danish chemical compagnies are as hard to tak to as I think....

Photo Engineer · May 6, 2008

I talked to one of the engineers who worked on glass plates and he said that nothing was as good as chrome alum for adhesion of emulsions to glass. It is also rather slow in action, as sometimes emulsions were stored for a few days with the chrome alum in them already. IIRC, this is mentioned in several text books.

However, the pH is critical in the coating. Too much acid or alkali will upset the effectiveness of chrome alum.

PE

Kirk Keyes · May 6, 2008

dwross said:
And, Kirk: magnesium carbonate and don't you dare laugh.

Magnesite? Dolomite? Chalk? Exlax??? Oh, for the flubber emulsion... OK, I promise not to laugh...

Kirk Keyes · May 6, 2008

Photo Engineer said:
[..] this is mentioned in several text books.

However, the pH is critical in the coating. Too much acid or alkali will upset the effectiveness of chrome alum.

More info please...

Photo Engineer · May 6, 2008

I'll leave that as an exercise for the student. Y'all have all of those textbooks.

Seriously, the pH should be about 6.3-6.7 for best results. To far acid and it does not work, and too far alkaline and it sets up too fast. I've had chrome alum melts set up just by adding some addenda.

Trial and error is all I can suggest right now.

PE

emulsion on glass: wetting agent or not...

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