Dag Help: Weak Images

[Bingtan]

Sorry to trouble you guys, I was working this weekend and having better results but more trouble along the way: Made a few 6×6 plates and Images were very weak. I can see them, great detail but very light, not fogged.

Details:

31C / 41% humidity

Fuming with fluorescent light from the room about 8ft away:

Iodine – golden yellow 1st cycle. Sometimes a few seconds more seeing a very light hint of rose.
Bromine – 2 mins and the color looks like this. I tried 1 min, 1:30 min, 2:00 min and 2:30 min.

I don’t see any noticeable difference in the image based on my Bromine to be honest except that at 1 min, it was even weaker.

Close the light:

Iodine – I did a 2/3 of first (mike robinson’s) I also did 1/3 of first.

Exposure:

ev 9. I was following pobboravsky’s exposure table: http://www.cdags.org/cdags_resources/pobboravsky_exposure_guide.pdf

but I’ve always been exposing 2 stops slower. so at 9 ev, table says 15 secs, I’ll exposure to 1 min.

Fuming:

Looking at about 68-70C for 8 mins.

I’m suspecting it’s not enough mercury but I’m not sure…my pot is big enough to fit a full plate (but not an 8×10) with about 80grams of mercury. My fume boxes will also fit a full plate but not quite an 8×10.

Would appreciate any leads…

Sincerely,

Bing

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[nawagi]

Are you making test strips?

Hg pots require very little mercury – about the size of a 1 Euro coin is plenty.
I cook at 80C for 4 minutes.

Bromine looks pretty strong – and you Br times seem very long.

If I were over your shoulder, I would suggest the following:
1st fume to 1st yellow
Br in 4 strips: 10, 20, 40, 80 seconds
2nd fume 30% of first fume time.
Expose a bright scene (EV 15 at ISO 100) at f 8 for 4 strips: 8, 15, 30, 60 seconds.
Hg Cook at 80c for 4 minutes

Evaluate the plate for the best white without solarization (determines bromine time) and best shadow detail (determines exposure time).

NWG

[jgmotamedi]

I agree with Nate, you need to work more on your Br/I balance. Plan on running quite a few test plates to get your bromine time. Once you get it down you will know what the color should look like, and can adjust for room temperature and weaker or stronger boxes. My current silica gel/bromine mix is much lighter than yours, and I am running it about 80 seconds.

I really doubt it is the mercury. It almost never is.

[Bingtan]

Thank you Nawagi / Jason,

seems to be the case. can I ask a stupid question, now that I’m getting to understand that the Bromine phase is such a critical step, bec it’s a phase that may not be visible to the naked eye but more of a time-based approach – is there a possibility in using a sensor to make it easier for practitioners to at least get insight if the bromine is too strong? I came across this manual detector that can detect up to 20ppm?

http://www.zefon.com/store/sensidyne-114-bromine-detector-tube.html

I mean in the long haul, at least you can tell if your beads are already exhausted (since I noticed that you really just need a very small amount of bromine apparently!)

[photolytic]

I use a bromine/lime mix that gives me a fuming time of 8 to 16 seconds at 20C

The vapor pressure of bromine at this temp (200 torr) should generate a vapor concentration of 1400ppm.

I took triplicate samples of the bromine vapor using a syringe equipped with a needle inserted through the pressure plate of the box where plate fuming takes place.

I converted the bromine to iodine within the syringe using an acidic solution of sodium iodide.
I did an iodometric titration analysis of these samples using sodium thiosulfate with starch indicator.

My results showed there was only a little over 1mg/l (1ppm) of bromine vapor at the top of the box.

I got even lower analyses (.01ppm) from my iodine fuming box where the vapor is even heavier.

Bromine vapor is heavy (2.5gm/cc) which probably allows for considerable vapor stratification in the box.

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[Andy Stockton]

Hi Photolytic-

Interesting info. How long does it take the vapor stratification to stabilize if a fuming box is left undisturbed? Is it stratification changes from mixing that contribute to changes in fuming times during a multi-plate daguerreotype session? (mixing from opening/closing the box cover etc.) I wonder if there is any way to control or compensate for that. Maybe it is contributing to the variability in Bingtan’s images?

Andy

[photolytic]

Andy,
If you consult Pobboravsky’s 1971 thesis posted in the resources area, you will note on page 40 that he broke up long fuming periods into as series of 60 second intervals with 60 second rest periods in between fuming to allow for the vapor levels to recover. I broke up my fuming box sampling by withdrawing a series of 50cc vapor samples with several minute intervals in between, during which I shook the vapor in the syringe with a solution of acid + sodium iodide to extract the bromine vapor from the air. In addition I ran the sampling tests in triplicate and got no more than a plus or minus 10% variation in results between samples.

Given the rapid speed of halogen molecules in the air, which increases with temperature, the vapor stratification should resume it’s equilibrium condition in a minute or less. The distance between the halogen solid or liquid and the plate, which was appox. 80 cm in Pobboravsky’s and my fuming boxes, would reduce the amount of stratification but not eliminate the effect.

The Clausius–Clapeyron equation can be used to relate the log (ln) of the vapor pressure of the halogen (or any other vapor) to to the log of the reciprocal temperature in degrees kelvin. (C +273). Plotting the log of the vapor pressures of bromine in the literature against the reciprocal temperature indicates that a +5C increase in temp approximately doubles the vapor pressure or vapor concentration.

The choice of using an 1840-1860 slide though fuming box design which offers minimal vapor loss and disturbance between opening and closings vs the more “modern” drop down lid type fuming box may be an important factor in deciding whether the operator is willing to live more vs less vapor disturbance during fuming.

Another possible variation may be the high humidity which often accompanies high temperatures in tropical regions. Bingtan makes no mention of this variable in his notes but most 19th Century operators report that water vapor is not desirable in fuming. Some suggest that water be removed by placing a dish of freshly slaked (melted) lime in the (iodine) box overnight. One might assume that silica gel does the same job here but eventually silica gel will become saturated with water which can not be remove without driving off the bromine at the same time. A dangerous and wasteful procedure given the cost of bromine to the Daguerreotypist.

[photolytic]

Correction: Fuming box depth quoted should be 80mm not 80cm.

[Bingtan]

wow…that is a lot of science into fuming…so yesterday, I did some practice. One of the things I realized is that a 6×6 plate is quite small compared to the size of my box which is good enough for an 8×10. As I did multiple fumings trying to test things out. 500gms of deeply “soaked” iodine silica beads is a lot, making fuming times really fast. so right now,

My box is lowered to just about 100 grams of iodine silica beads giving me about 20-25 secs for first yellow. Any longer and I start seeing reds which quickly goes into blue at around 40 secs.

For bromine, I lowered it from 500 grams to 250grams. I think it is now at the right color/dilution of light yellow beads. I will start fuming again next week, getting a grasp for all of these things.

The iodine part, sure I understand it needs practice but it’s quite visual. It’s the bromine that I’m worried about because I can’t judge it visually but by time. I think this is where I’m going to need a lot more practice. Since I’m practicing heavily by rotating some 6×6 plates, I will be working on Nawagi’s Bromine fuming suggestion of a 10-20-40-80secs in 2 plates.
Bing

[Andy Stockton]

Hi Bingtan – I’m really glad you got this thread going. Photolytic’s background as a professional chemist makes him a unique contributor to the world of contemporary daguerreotypy. Anyone who is looking to understand the science behind the process should read and re-read his posts and publications along with those of Irv Pobboravsky. They are really helpful for getting your process parameters under control.

Photolytic – a question about humidity. Do you find that the slaked lime also eventually becomes water saturated, or does it have significantly different properties compared to Mike Robinson’s suggested use of silica gel? I have wondered if there is a way to achieve some drying of either by perhaps putting a watch glass of fresh chemical in the box overnight? I thought the differential in saturation might promote some drying without completely wasting the active Br or I. Is my understanding of the chemistry involved off-base?

And Bingtan – my apologies if this is hijacking your thread. I can split off the questions if you are not finding this helpful.

Andy

[Bingtan]

Andy, don’t be silly, being new, I am trying to understand things as fast as I can on top of which, you guys would be smarter at asking the right questions which I may not understand. Can you share w me how you use slake lime? An idea of proportions including rough size of the container it’s held in?

By the way, just call me Bing 🙂

[Andy Stockton]

Hi Bing – The process does have a steep learning curve. 🙂 I believe slaked lime is used in a similar way to silica gel, but I haven’t used it myself so perhaps someone who has can fill you in more.

Andy

[photolytic]

Slaked lime like any deliquesent salt absorbs water until it liquifies, at which point it stops working but can be regenerated by heating to drive off all the moisture. Put it in as large a dish as will fit in your box and remove it when it is time to fumed a plate.
I suppose Dry Rite (calcium sulfate) would work too. Another possibility is a small pore size molecular sieve.
Molecular sieves are synthetic porous crystalline aluminosilicates which have been engineered to have a very strong affinity for specifically sized molecules. The definitive feature of the molecular sieve structure, as compared to other desiccant medias, is the uniformity of the pore size openings.

Number 3A molecular sieve, which has a 3 angstrom pore opening, allows polar water vapor adsorption (size 2.75Angstroms. whereas the non-polar bromine molecule is only 1.2 Angstroms so it doesn’t look like Br2 would be excluded.

[Bingtan]

Hi photolytic,

On my notes, our current humidity is around 41% when I was fuming

1) Slake lime is calcium hydroxide (just making sure)
2) Correct me if I’m wrong but slake lime is placed inside the fuming box when you don’t have any iodine or bromine in the box to take out the moisture?
3) I don’t take out the silica beads (I & Br) in my fuming box. Is slake lime something I can introduce into a box with I & Br Beads to help take out the moisture? The slake lime is introduced in the box to take out the humidity? Won’t it absorb both the I and Br or only just water?

Bing

[photolytic]

You slake calcium hydroxide by heating it to the melting point to drive off any water of hydration.
The slaked lime is then placed inside the box to remove water from the iodine crystals and silica gel too.
It does not adsorb the water on it’s surface like silica gel does.
It removes water by forming a hydrated salt.
It does not form any salt with pure iodine of bromine alone.
It will form a salt only if there is any hydroiodic (HI) or hydrobromic acid (HBr) in your box.
HI or HBr can form if Iodine or bromine are mixed with water when hydrogen sulfide is present

[nawagi]

B-

You have two terrific ‘scientific’ instruments: your eyes. Bromine fuming changes the surface color of your plate over time (just like I). Training your eye to color changes will allow you to adjust for different strengths of fumes in each box. The Br step test I mentioned is an aide in training your eye: look at the plate after each step and you will see this; memorize the color and you will use it.

Be wary of “rote” – just because 30:06:10 works on Tuesday does not mean it will work on Wednesday. But straw:first magenta:10 on Tuesday almost always works on Wednesday. John has a distinct advantage over me- 1) he’s a genius and 2) he has a true scientific lab. He also has 10 times as much “time in the saddle”. Not to put too fine a point on it, but my 100th plate was a heck of a lot better than my 10th (can’t wait for number 1000! eta: 2020)

Humidity is very problematic in dags- for buffing and fuming especially. I run a dehumidifier in my lab all summer to keep the RH at around 50 – 55%. Even then, a walk outside into the very humid Connecticut summer air can wreak havoc on a plate. But I always think about our 19th century operators- they had slaked lime; a different solution tot he same problem.

BTW,I started with Br and Lime but changed over to Br and silica gel- less of a mess and easier to get a consistent color without so much “up close and personal” face time over the toxic fumes.

NWG

[Bingtan]

Photolytic,

That is incredible information for me which will be extremely helpful for my more humid environment. I will take that advice and bring in some slake into my fuming boxes. May I ask for a nice ratio/proportion? I use those “standard” 11-cup pyrex trays a lot of people seem to be using. How much calcium oxide:h2o -> calcium hydroxide should I introduce as a starting point? say 200grams CaO + 40ml H2O?

Also, If the slake acts as a “dehumidifier”, is there any reason to take it out of the fuming box? Why not just leave it inside the box?

Nwg,

I’m slightly confused in that, not all Br fuming actually shows a color change. So I was under the assumption that I may have really have to nail down a time…which obviously makes things a lot more difficult. Ok, I shall try to see the color changes in Br given your suggestion. I’m hoping I see it as distinctly…bec honestly, I couldn’t see the change in color of Br on my plates. Iodine, I can. It’s very distinct.

[photolytic]

Don’t add any water with the Cao. 200 grams of Cao is probably too much.
You don’t want Cao dust to get on the plates or it will make spots
If you have calcium hydroxide, heat it first to drive off the water before putting it into the fuming box.
The dish of slaked lime will cover too much of the halogen and must be removed before fuming to allow the halogen to contact the plates.
The color changes in the bromine are not very strong. The effect is most noticeable after the 2nd iodine fuming.
The silica gel will act as a dehumidifier also but may already have too much water in it.

[Andy Stockton]

Photolytic-

Will the calcium hydroxide actually pull water from the silica gel, or will only heating accomplish that?

Andy

[Bingtan]

Andy,

it seems like CaO will pull water from the fume box > including the water contained inside the silica gels (aside from I and Br).

When the CaO gets saturated, that is what you heat to dissipate the water absorb by the powder.

[Bingtan]

Andy,

it seems like CaO will pull water from the fume box > including the water contained inside the silica gels (aside from I and Br).

When the CaO gets saturated, that is what you heat to dissipate the water absorb by the powder.

So it seems like CaO is acting like the dessicant of the dessicant (silica gel).

[Andy Stockton]

Hi Bing-

That’s what I was thinking too. I’m not sure about the chemistry though, thus my question to photolytic. I’m not clear if the silica gel will release water simply because there is a differential between the saturation of the gel and the CaO. I am unclear on the process by which silica gel absorbs and releases water – it may be that it will only release water if heated.

Andy

[Bingtan]

If humidity is high inside the box, the silica gel will keep absorbing water – competing with the I and Br inside. The only way to release the water inside the gel is to heat it but when that happens, I and Br also gets released, or even before that…

According to photolytic, by putting CaO, it can act as the H2O replacement dessicant instead of the Silica beads thereby keeping your beads busy in just absorbing I and Br. CaO only attracts I and Br when they are in HI and HBr form.

If the silica beads are heavily saturated by H2O already, I don’t think the CaO can do much about it..

[Author]

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