From: Richard Knoppow on 24 Aug 2007 02:00
"Geoffrey S. Mendelson" <gsm(a)mendelson.com> wrote in message
> dan.c.quinn(a)att.net wrote:
>> the darkroom. I've a few orange-ish yellow safelights.
>> Very easy to
>> see and do in my darkroom. Dan
> Speeaking of that has anyone tried to put a compact
> flourescent bulb in
> a safelight? I assume if it would work, the safelight
> would have
> much farther from the paper than with an icandescent one
> of the same
It would likely work but the compact fluorescent lamps
are all quite bright compared to low power incandescent
lamps. Another possibility is to use an array of LED's.
There has been a lot of discussion of LED safelights, do a
google search for it.
Los Angeles, CA, USA
From: Richard Knoppow on 24 Aug 2007 02:18
"Rod Smith" <rodsmith(a)nessus.rodsbooks.com> wrote in message
> In article <slrnfcqdel.65c.gsm(a)cable.mendelson.com>,
> gsm(a)mendelson.com (Geoffrey S. Mendelson) writes:
>> dan.c.quinn(a)att.net wrote:
>>> Agfa for many years recommended a 2% solution
>>> of sodium carbonate. Dan
>> Ok, I'll look for those things, but it's not a priority.
>> In 2003 I bought
>> large bottles of Tental developer, wash aid and fixer.
>> The developer
>> did not last, but the fixer and wash aid concentrates
>> seem to be
> Wash aids tend to deteriorate over time, so unless you've
> got a way for
> testing activity, I'd be a bit cautious with the wash aid.
> Fixer develops
> a spoiled-egg smell when it goes bad, although I suppose
> that might be
> masked by an ammonia odor with some fixers.
> As to sodium carbonate, that's a VERY common ingredient in
> detergents. In the US, Arm and Hammer Washing Soda is pure
> carbonate monohydrate; I use that in my formulas that call
> for it. You
> might be able to find sodium carbonate sold as a laundry
> booster in
> Israel, but I don't know your local brands, so you'll have
> to check box
> ingredients yourself.
> Rod Smith, rodsmith(a)rodsbooks.com
> Author of books on Linux, FreeBSD, and networking
Fixer will eventualy decompose. When it does it has a
strong sulfur odor but also usualy has a deposit of
precipitated elemental Sulfur in it. It can be yellow or
cream. It has to be pretty far gone for this.
Acid fixer is much more likely to decompose than plain
fixer but both have a limited life. Even rapid fixer
concentrate has a limited life, perhaps because most of it
comes in plastic containers which are permeable to air.
The sulfite in wash aid will slowly oxidize to Sulfate.
The sulfate does no harm but does not have the washing
accelerating properties of Sulfite (or at least it has them
in much reduced amount).
Its hard to know how long the life of a wash aid
concentrate is. The Kodak product is about 10% Sulfite and
Kodak gives its shelf life in a filled, sealed, container as
6 months. Kodak tends to be conservative about shelf life
but, since wash aid gives no sign of being oxidized, its
good practice not to keep it for too long. Working strength
wash aid is strictly an expendible and should not be saved
and re-used. Its life in a tray is several hours.
Los Angeles, CA, USA
From: Geoffrey S. Mendelson on 24 Aug 2007 02:29
Richard Knoppow wrote:
> It would likely work but the compact fluorescent lamps
> are all quite bright compared to low power incandescent
> lamps. Another possibility is to use an array of LED's.
> There has been a lot of discussion of LED safelights, do a
> google search for it.
The advantage of compact flourescents is that they are very common
here and relatively cheap. I looked around the local shopping mall
(the largest in the "middle east") and the local hardware store.
At the mall I was unable to find anything, at the hardware store
I found 15 watt bulbs with a small base (no adaptors available)
for refigerators and sewing machines and 5-10 watt bulbs that fit
it. The lamp base is part of the safelight, it's a Kodak cone
shaped grey metal can with a lamp socket at one end and a filter
at the other.
Unfortunately I have no way of telling what their wattage really is, my
AC ammeters don't go that low.
I'm no longer sure who recommended the Kodak publication "How safe is
your safelight" (I think it was you Richard), but I can not find
it on line. A search of their web site shows several references to it,
but not the document itself. :-(
LED safelights are definitely a possibilty, I have many red LED's
and the necessary skill to wire them togther.
Yesterday, my youngest son came down and saw the enlarger and said
"ooh a camera, let's do it", so there may be hope yet. :-)
Geoffrey S. Mendelson, Jerusalem, Israel gsm(a)mendelson.com N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http://geoffstechno.livejournal.com/
From: Richard Knoppow on 24 Aug 2007 02:54
<dan.c.quinn(a)att.net> wrote in message
> RE: On Aug 22, 11:48 am, Peter wrote:
>> I suppose there would be a few more options for
>> a wash aid although some ingenuity may help.
> Agfa for many years recommended a 2% solution
> of sodium carbonate. Dan
So did Kodak. This is the result of research carried out
by Edith Wyde at Agfa labs in the 1930's. The alkali works
because it changes the pH of the gelatin to a point above
(more alkaline) than its "isoelectric" point. This changes
the electrical charges on the molecules in a way that
rejects Thiosulfate ions instead of attracting them.
Unlike many other substances Gelatin has no definite pH.
Rather it has the properties of both an alkali and an acid.
This is called being Amphoretic. Gelatin tends to have the
pH of the last bath it was treated in. Nonetheless, the
molecular charges in Gelatin are dependent on whether the pH
is higher or lower than its isoelectric point (where the net
molecular charge is zero). When it is on the acid side the
charges are opposite to fixer and its reaction products so
their ions tend to be attracted to and held by the gelatin
molecules. By adjusting the pH to a point on the alkaline
side of the isoelectric point the charges are reversed and
repel the unwanted ions, thus accelerating their washing
The isoelectric point of gelatin depends on how it was
manufactured. For most photographic gelatin the isoelectric
point is just slightly on the acid side of neutral.u
The alkaline condition also has an effect where a White
Alum(Potassium Aluminum Sulfate) hardener has been used. The
Alum tends to bind the Thiosulfate ions and the silver
complex ions to the gelatin in a way similar to the mordant
used to prevent the running of dye. Again, this effect is pH
dependent. It is most effective in a fairly narrow pH window
on the acid side of neutral. The alkali bath changes the pH
of the gelatin to a point where this mordanting effect is no
longer active. However, most alkalis, such as the
Carbonates, or Borax, move the pH far enough to the alkaline
side to break the cross-linking of the hardening so the
hardening is also no longer effective.
Sodium Sulfite is also a weak alkaline and has the above
effects on Gelatin. However, most of its accelerating action
on washing is due to another effect called ion exchange. The
Sulfite ions are taken up the gelatin preferentially to the
Thiosulfate ions and Thiosulfate-silver complex ions
resulting from fixing so these are actively displaced. In
Kodak's research no other substance tested had the
ion-exchange property to the same extent as the sulfites.
Other sulfites, such s Ammonium Sulfite, can be used, but
the sodium salt is common and easy to obtain. Also, Ammonium
salts tend to be unstable in solution.
Kodak Hypo Clearing Agent is buffered to neutral. This is
so that it will preserve the hardening action of white alum
hardener but break its mordanting effect. Neutral pH is also
far enough away from the isoelectric point of photographic
gelatin to reverse the charges on the molecules and repel
the Thiosulfate ions and fixer reaction products which may
be bound up to the gelatin and image silver electrically.
Another advantage of conditioning the Gelatin to neutral
pH is that its swelling is minimised. The swelling of
gelatin is dependant on its pH compared to its isoelectric
point. The swelling is minimum at the isoelectric point.
Kodak, in one of its reseach papers, states that the rate of
diffusion of the unwanted ions is partly dependant on the
swelling of the Gelatin. While it seems intuitive that the
rate should increase with swelling in fact it is the
opposite. The diffusion rate is dependant on the diffusion
path, which is minimum when the Gelatin is _not_ swelled.
Kodak Hypo Clearing Agent also contains two sequestering
agents to prevent a deposit of Sulfite, Aluminum (from the
hardener) and mineral salts from the water on the film or
The patent shows only one of the sequestering agents,
EDTA Tetra-Sodium Salt, but the MSDS shows the commercial
product also contains some Sodium Citrate. Otherwise an
effective wash aid may be made from 2% Sodium Sulfite, or if
he buffered version is desired, add some Sodium Bisulfite
(or Sodium Metabisulfite). The patent formula shows:
For one liter of concentrate:
Sodium Sulfite 100.0 grams
Sodium Bisulfite 15.0 grams
EDTA Na4 5.0 grams
Water to 1.0 liter
Dilute 1 part concentrate to 4 parts water for use.
The amount of Sodium Citrate in the commercial version is
not known but is probably the same as the amount of EDTA.
Los Angeles, CA, USA
From: Claudio Bonavolta on 24 Aug 2007 05:13
On 24 août, 08:29, g...(a)mendelson.com (Geoffrey S. Mendelson) wrote:
> I'm no longer sure who recommended the Kodak publication "How safe is
> your safelight" (I think it was you Richard), but I can not find
> it on line. A search of their web site shows several references to it,
> but not the document itself. :-(