two kinds of Multigrade filtering?

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Tony Clarke - 21 May 2007 20:14 GMT

I've been using Ilford Multigrade paper and filters for years, with the
filters, in the above-neg position, being the usual (so I hitherto thought)
range between 1 and 6 in 1/2 grade increments, ranging in colour from a
light orange to a dense pink.

However, recently in a charity (thrift) shop, I picked up an Ilford set
thinking it would be good for my new large-format enlarger which needs an
under-the-lens filter holder which this box has. On examining it, I see it
looks rather older in design, says Ilfospeed Multigrade on the box, and the
filter inserts are graded 1 through 7 in whole grades and range from a pale
tobacco green (grade 1) through nearly colourless (3) through mauve to a
dense purple (7). The calculator dial that was in the box gives least filter
factor for the 3 - about half a stop - and higher amounts towards the ends
of the range. My existing ones seem to have a slightly rising filter factor
per grade, or at least for the pinker (hard) grades.

What have I got here? An earlier incarnation of Multigrade, or something
optimised for a different lamp spectrum? (I understood the principle of
Multigrade was balancing two separate green-sensitive emulsions through
differential spectrum control, is that correct?). My regular enlarger is an
MPP condenser with the standard 100W pearl bulb, and MGIV paper prints and
grades just fine using the orange/pink set. I've not yet tried this new lot
on a print yet to see what it actually *does*.

Further information greatly appreciated!

Tony Clarke

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Richard Knoppow - 21 May 2007 22:25 GMT

> I've been using Ilford Multigrade paper and filters for
> years, with the
[quoted text clipped - 41 lines]
>
> Tony Clarke

Curious, if the filters have not just faded they would
still be transmitting the same colors to the paper. Modern
VC paper has two emulsion components (Ilford has three), a
low contrast one sensitized to both blue and green and a
high contrast one sensitized only to blue. For low contrast
one exposes using green light, which the high contrast
emulsion does not see, for high contrast both emulsions are
exposed by using a filter which transmitts only blue light.
For increased visibility of the image on the baseboard this
is a magenta color-difference filter (transmitts all colors
except green) rather than a green filter. Modern filters are
also balanced so that the effective paper speed remains
constant although in two ranges, one for grades up to 3.5
and the other, half the speed, for higher contrast. Earlier
filters required a change in exposure for each grade. I
suspect what you have is a very old set of filters. It may
work on modern paper but the grade spacing may not be right.
Also, both Ilford and Defender (later Dupont) made the
first variable contrast papers, along about 1940. I am not
sure of the Ilford paper but the colors required for the
Defender paper were the reverse of modern stuff.

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---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com

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Tim - 23 May 2007 02:40 GMT

> [...] the
> filter inserts are graded 1 through 7 in whole grades and range from a pale
[quoted text clipped - 3 lines]
> of the range.
> [...]

Multigrade papers work by combining green and blue sensitive emulsions.
Your filters vary from transmitting green light, through to
transmitting blue light (plus red, which of course doesn't contribute to
the exposure). So it sounds as though they will work perfectly well.

I guess this is an early version of multigrade filtering, which was
later replaced by filters which don't need the exposure calculator.
"Normal" filters also transmit red light (the low-contrast filter is
yellow, vs your green filter), which helps make the image more visible
without affecting the exposure.

There's a history of Ilford Multigrade at
<http://website.lineone.net/~mauricefisher/Darkroom/Multigrade.html>
Though it doesn't mention a system with green filters, it's interesting
to see that the order of the filters has changed, with earlier versions
of multigrade used yellow filters for the hardest contrast grades.

-Tim

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Richard Knoppow - 21 Oct 2007 16:51 GMT

>> [...] the
>> filter inserts are graded 1 through 7 in whole grades and
[quoted text clipped - 29 lines]
>
> -Tim

This thread is getting quite old but I will add to it
anyway:-)
The above article is very interesting. Ilford variable
contrast paper had sensitizing reversed from the current
type. I had thought that Ilford changed this in the early
1960's the article indicates the change was much more
recent. The filers asked about seem to be for the older
system where the blue only sensitized (non color sensitized)
component was low contrast and the blue and green sensitized
component was the high contrast one. This is the reverse of
VC papers made over the last about 25 years. Both current
Ilford and recent Kodak filters are for the system where the
blue component is the high contrast one.
I should also note that Defender Photo Supply in the USA
had Varigam on the market about the same time as Ilford
Multigrade, i.e., 1940. I think Varigam used the current
system but am not sure. Defender had ties with both Kodak
and Dupont (who eventually bought the company). Defender and
Ilford must have been aware of each other's work.
The idea of introducing some neutral density into the
filters to equalize exposure is also quite recent, about 15
years ago I think.
The usual variable contrast filters are complimentary
rather than having the color of the light needed for
exposure at a given grade. The idea is that the visual
illumination at the baseboard for focusing and composition
is much brighter.

Signature

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com

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Nicholas O. Lindan - 21 Oct 2007 19:09 GMT

> The filers asked about seem to be for the older system where the blue only
> sensitized (non color sensitized) component was low contrast and the blue
> and green sensitized component was the high contrast one.

The way I understand the way the system works is that there
are two identical low contrast emulsions.

Both are sensitive to blue. One has a sensitizer added
to make it sensitive to green as well as blue.

Exposing one low contrast emulsion with green light gives a
low contrast print.

But exposing with blue light, to which both emulsions
are sensitive, gives a high contrast print.

Intermediate grades are made by exposing various proportions
of blue and green.

HD diagrams of VC materials often resemble a bumpy roller
coaster ride because of the vagaries of the green sensitizer,
the difference in the characteristics of the two emulsions
and the match between contrast filters and emulsion sensitivity.

Ilford adds a third cyan & blue sensitive emulsion to
smooth out the response and expand the contrast curve.
Green light exposes one emulsion, cyan exposes two
emulsions and blue exposes three emulsions.

If you look at the colors of the Ilford filter set and
a CIE color diagram (or other 2-d representation of 3-color
space) they form an arc, centered at red, going from orange
to magenta. Grade 2 is a dusty pink - a combination of red
and neutral density - on the line from red to the white center
point.

http://www.henrysturman.com/images/cie.jpg

Information is from Mees and Ilford product literature.

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Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation: F-Stop Timers, Enlarging Meters
http://www.darkroomautomation.com/index.htm
n o lindan at ix dot netcom dot com

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