On Wed, 29 Jan 1997, Terry King wrote:
>> With the more highly reflective colours, eg yellows, you need more
>>pigment
>> to get contrast but more pigment decreases the effectiveness of the
light.
.> In general strong pigments, where you need less of it to achieve the
same
>> effect, will be of benefit.
.
>Terry, I'm not insisting that you take a Trappist vow of silence, far from
>it, but you are simply wrong in this.
>I mean not just wrong in confusing "contrast" with chroma, and both
>with covering power, but wrong....
>For instance 5 different yellows seen on the paper have the same quality
>of what you call "reflectivity." Their *covering power* and hence the
>amounts of each needed to get that color in a print varies widely.
That, Judy, is just what I am saying. I am not disagreeing with you . I am
right and you are right. Lets not call the whole thing off!
>The
>covering power of arylide yellow, for instance, is greater gram for gram,
>not simply than many other yellows, but for all its "reflecctivity"
>greater than either thalo blue or quinacridone red.
That is another way of saying what I said.
>This is seen in the
>fact that smaller weights of the yellow are needed to balance tricolor
>gum. I say this with confidence because I have weighed the pigments.
Yes
>Weighing pigment, I must add, is hardly more effort than squeezing alone.
You must be joking.
>Put a little plastic airline desert dish on the pan of the scale. (Mine is
>Alaska airlines, weighing 24 grams). Start with the marker balanced at
>this weight. Then slide marker up to add the amount of pigment you want,
>squeeze paint into the dish until the needle again balances. Add the rest
>of ingredients as usual. Dish is wide enough to take the foam applicator.
>No waste, as there is inevitably in trying to lick emulsion off a plate
>with a brush.
That technique sounds fine for single colour but pigment gets lost in the
foam brushes. For more than colour use a plate.which enables you to see the
strength of the mix of different colours.
>But again, speaking of "reflectivity", so called, of paint, we might feel
>that various blues -- prussian, indigo, ultramarine, permanent, thalo,
>etc. -- "reflect" light similarly, but they are vastly different in
>covering power. Indigo, for instance, would take a fraction of the bulk of
>some of the others, as you well know (especially as you sent me to
>indigo).
That is just the point. Use strong colours and you get less interference
with the light.
>> There is an aternative approach that can give more information, in the
>> context of the multicolour print, and that is making a work print stage
by
>> stage in advance of making the final print.
>Hello? Would you please explain the difference between that and making a
>gum print? I mean every multicolour print advances stage by stage.
Again that is just the point. I an sure that we both appreciate that the
perceived colour from a mixture depends upon the varying proportions of a
colour within a mixture. These proportions are going to change across the
picture area dependent upon the proportion of tonal values in the negative
being printed.
>Sometimes there are false starts, and sometimes great discoveries, but
>doing the same thing twice would be as boring as...... platinum printing?
It is just because there are false starts that the work print gives a guide
as to the proportions and pigments and lengths of exposure that one wishes
to use in the final print. This trial elemnt is as exciting as platinum
printing where one uses differing proportions of different chemicals to
achieve a particular effect.
>> funnily enough, Gloy/ammonium dichromate
>> seems to be about three times as fast.as potassium dichromate/gum
arabic.
>> At least it was when I had to scour a town for materials after a college
>> pleaded that its gum arabic and potassium dichrmate had not been
delivered
>> for my workshop. My demonstration with the, then absolutely new to me,
> >Gloy/ammonium dichromate grossly over exposed compared with my usual
> >practice. I had to reduce the exposures to about a third before the
> >combination would work.
>My tests showed speed of gloy to be about the same as for gum. I'd say the
>speed change you describe above was due to the ammonium dichromate, not
>the gloy.(You changed 2 variables at once & leapt to an assumption.) In
>any event, I doubt speeds of the kind we're talking about matter so much.
I checked to find that Gloy is somewhat faster. But I was comparing gloyam
against gumpot.
>my friend's problem was *30* minutes, another order of magnitude entirely.
Not knowing the light source and other variables I would suggest that a
thirty minute exposure could be much too long. Under the sun bed the
exposure can be as short as one minute but when I first started I remember
an exposure under November cloud taking two days.
>, tho I once had an actuary in a workshop who demanded to
>know it & didn't think much of me when I couldn't supply it. (I should
>have made one up & told him he put in too much/too little pigment.)
You would almost certainly have been right.
>The Terry King medal for service to the field!? Oh, oh, I can say no more,
I just wanted you to come to the Spring meeting !
Terry