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View Full Version : Can Anyone Answer Me This Question (Chemistry/Common Sense Related)


M.L. Schaefer
03-14-2013, 10:44 PM
Now, I love to mix my coffee, a good regular blend mixed with a bit of chocolate flavored blend. If I were to mix the same amount of Regular Blend Coffee + same amount of Water = Strong Coffee. The same with Chocolate Blend + same amount of Water = Strong Coffee. Mix the two together + same amount of Water = Strong Coffee with a different flavor.

Time and again, I've heard tell that if you mix pigment ranking No. 1 in lightfastness with another pigment ranking No. 1 in lightfastness and, voila, you get a lower lightfastness!!???

My common sense (foregoing my much to be admired and desired math skills) tells me mixing a No 1 in lightfastness + a No. 1 in lightfastness = a No. 1 in lightfastness, but with a different color flavor.

What's the deal. It seems 1 + 1 doesn't always = 2???!!!! Or where are my "math" skills going wrong :lol: :lol: !

:heart: Margarete

FLNH
03-14-2013, 11:07 PM
I understand your logic, but you are assuming that light fastness is a simple additive quality and it probably is not. For example, if you mix 50 oz of water with 50 oz of alcohol you really do not get 100 oz of liquid.

Another ( and better) example, cosmetic creams are complex mixtures. If cream A has one kind of preservative and cream B has a different preservative system and you mix equal parts of the creams, you dilute both preservative systems to 1/2 strength and you may lose preservative effectiveness for the mixture of the two creams. I suspect that whatever produces light fastness in one tube of paint is not the same in a different paint and this may account for the decrease in LF
for the mixture.

Hope this helps.

M.L. Schaefer
03-14-2013, 11:21 PM
Hi, Karl! Yes it does make sense. Better rationale than mine.

May I add: "and in this lies madness" :lol: :lol: :lol: or "much ado about nothing!"

:heart: Margarete

Yorky
03-15-2013, 03:51 AM
I would say if a pigment is inherently light resistant mixing it with another won't change that. However mixing it with a non light resistant pigment wont stop that pigment fading so overall the mixture will show some fading.

Doug

seedy
03-15-2013, 11:16 AM
" For example, if you mix 50 oz of water with 50 oz of alcohol you really do not get 100 oz of liquid"
Well now....what do you get? That"s the way I always mix my Gin and Tonics....and guess what I get?.......;-)

FLNH
03-15-2013, 11:18 AM
....a little less than you thought. You need to drink more.:) :)

Mike3839
03-15-2013, 11:39 AM
Margarete, whatever formula you use it's still gonna turn out mud. :D:lol: :D.

Mike

M.L. Schaefer
03-15-2013, 02:34 PM
My coffee :lol: aint that bad, Mike!!!

:heart: M.

CharM
03-15-2013, 04:00 PM
I understand your logic, but you are assuming that light fastness is a simple additive quality and it probably is not. For example, if you mix 50 oz of water with 50 oz of alcohol you really do not get 100 oz of liquid.

Wait a minute... what do you get then?

FLNH
03-15-2013, 05:30 PM
Approximately 96 oz. of liquid. I remember this from high school, but I did recheck it on the Internet by Googling. I'm better at chemistry than doing a link with my iPad.

http://www.newworldencyclopedia.org/entry/Ethanol

This might work
:)

Superturtle
03-16-2013, 01:36 PM
But that 4 oz difference is pretty negligible, wouldn't you say? It's close enough that in most situations, for most people, it's close enough to 100 for their purposes. And 96 or 100 ounces, you'll be too drunk to notice the difference anyways. :thumbsup:

As for the original question, the only way I could see two lightfast pigments mixing and becoming less lightfast is if they chemically react with each other to form a new chemical with a different structure with different properties. From what I understand, paints are pretty inert and don't really react with each other, so I don't think my reaction scenario would actually happen. If you're using paints with different binders, MAYBE, but the binders seem pretty stable as well (if they weren't, watercolor wouldn't store as well as it does). I'm dubious of this 1 + 1 = 1.5 logic. I'd have to agree with the folks saying that the mixture should be as lightfast as its components.

Mayberry
03-16-2013, 04:06 PM
I haven't heard this before. Where are you finding this information?
I know there are a few pigments that should not touch each other, like a lead pigment (lead white) with a sulfur pigment (ultramarine or cadmium), or prussian blue with zinc white. Or cadmium with certain copper-containing pigments. http://www.jcsparks.com/painted/pigment-chem.html (nice chart at bottom)

But why would mixing two lightfast colors together as a rule give less lightfastness? Does not make sense. I understand that using a pigment thinly will cause it to fade faster, because there is so much less of it than when you use it full strength. Are people saying that mixtures of pigments fade faster because there is a relatively low concentration of each individual pigment in the mix? This also does not make sense, unless there is some weird chemical interaction going on.

I'd like to see lightfastness test results of this claim, in cases where the two (or more) pigments are not already known to be chemically reactive with each other. Or images of paintings where passages have faded where known mixtures of otherwise lightfast pigments were used. Do people claim this decrease in lightfastness occurs when multiple colors are layered in watercolor glazes?

(And I'm here drinking my coffee with cocoa powder and a pinch of sugar added, topped off with milk. I drank it too fast for it to fade.)

M.L. Schaefer
03-16-2013, 05:45 PM
I've seen this a couple of times on the net (not WetCanvas) could be someone blogging etc without knowing the facts of the matter. Didn't make sense to me either...All my watercolors are either I, rarely II (which doesn't worry me a bit). I rely on a lot of my own "super-dooper-mixes), so I really wanted to clarify this even though it didn't seem to make sense to me. Most especially if I mix a I + II (I had always supposed it would make a II. If it made a III, then tears would roll down my cheeks!).

mmmmmm, coffee plus chocolat! Will try that, the coffee flavored one is artificially chocolate flavor, and I've been staying away from stuff like that...the chocolate flavor is a weakness!

Margarete

Quinacridone Gold
03-18-2013, 02:51 PM
I suspect that the truth is that if you mix a I and a III you won't get a II - it will still be a III. Not that we are using and III to start with, so if all your paints are I and II I can't believe there's a problem!

virgil carter
03-18-2013, 06:18 PM
M, your situation is clear: you need a chocolate with greater lightfastness. Perhaps you want to start a study of chocolate?

I humbly will leap into the gap on this one...

Sling paint,
Virgil

M.L. Schaefer
03-18-2013, 09:07 PM
Oh, Virgil, Sweetie! I crave chocolate, shouldn't have it...ha! say I. Too many yummy thoughts to let it go....too good to test it on a windowsill!

:heart: M.