two kinds of Multigrade filtering?

Discussion in 'Darkroom Developing and Printing' started by Tony Clarke, May 21, 2007.

  1. Tony Clarke

    Tony Clarke Guest

    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
     
    Tony Clarke, May 21, 2007
    #1
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  2. 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.
     
    Richard Knoppow, May 21, 2007
    #2
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  3. Tony Clarke

    Tim Guest

    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
     
    Tim, May 23, 2007
    #3
  4. 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.
     
    Richard Knoppow, Oct 21, 2007
    #4
  5. 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.
     
    Nicholas O. Lindan, Oct 21, 2007
    #5
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