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Mike L
06-10-2015, 11:27 AM
I checked the nearly two dozen varnish messages in the Umbrella thread and did not see an answer. I've also checked several art/craft supply websites (Michaels, Jerry's, etc) and even went so far as looking for the answer on W&N and Golden's websites and didn't see the answer there. I'm blind in one and and can't hear out of the other, so maybe I just missed it. :crying:

Drum rolllllllllllllllllll.

The Question - How long after the surface of an acrylic painting is dry to the touch is the paint considered cured, especially very thick applications? (I know, I know, it's hard to cure a disease that doesn't exist, but what can I say? :lol: :lol: :lol: )

Thanks in advance.

R/Mike

Andre Yusin
06-10-2015, 11:37 AM
I think it's up to 3 days generally, but who knows considering your particularly thick application. Search liquitex, they might have an answer.

bluefish
06-10-2015, 11:44 AM
a lot has to do with climatic conditions...a paint layer is going to dry quicker in Santa Fe then the same paint layer in Orlando.....remember Acrylic paint is porous....so the moisture will eventually filter it's way out....but a thick layer will take a lot longer for that to happen than a thin layer....because the answer varies based on the above, you will never get a diffinitive answer....sorry but those are the facts of acrylic paint life....

Davkin
06-10-2015, 12:38 PM
As the others indicate, "it depends". If the paint is especially thick and you live in a humid environment I'd wait at least two weeks, perhaps even a month to be sure. If the paint is thin and you live in a dry environment three days is probably plenty. Those are the two extremes as I see it, but I'll admit I have no scientific evidence to support my theories. :D

idylbrush
06-10-2015, 02:04 PM
This may answer your question.

http://www.goldenpaints.com/technicalinfo_drying

cliff.kachinske
06-10-2015, 02:41 PM
You didn't ask this, but I'll throw it in at no extra charge.

Be careful about heating paint film, especially if it's thick. If the water in the film boils it will pop through the surface and leave a pin hole.

Sticking your painting in front of a space heater will almost certainly cause this, in addition to the fire hazard. A heat gun on high will do this too unless you are very, very careful.

Mike L
06-10-2015, 05:13 PM
This may answer your question.

http://www.goldenpaints.com/technicalinfo_drying

It didn't give any time frames, but it sure gave a lot of information I didn't know. Thanks! :thumbsup: :thumbsup:

R/Mike

bluefish
06-10-2015, 06:19 PM
Mike...Golden nor any paint company cannot give you an answer....it depends on the relative humidity, paint thickness, etc.....to many varibles to give a firm answer....so wait, the longer you wait, the dryer the painting will be....

I've always said " I paint in the morning, sell it in the afternoon, then go fishing"...a joke about the quick drying properties of acrylics...but just a 'joke'...:wave:

idylbrush
06-10-2015, 08:35 PM
For very thin films, this time may be a few days, while films of 1/4 inch thickness or more will take months and even years to be completely dry.

JimR-OCDS
06-10-2015, 09:05 PM
I give my paintings about a month before I varnish them.

Mostly, because I can still make a change if suddenly a change is needed.

After varnishing, changes are not easily done, and for myself, I would never bother.


Jim

lowesguy
06-10-2015, 10:28 PM
My painting now are thin,dry overnite then next morning I apply clear coat X2 of latex base faux finish,lays down flat and flexible. makes the painting pop! when I can afford it will try the Golden acrylic polymer varnish,that's what the expert told me to use at Dick Blick.

Mike L
06-11-2015, 08:16 AM
...

Sticking your painting in front of a space heater will almost certainly cause this, in addition to the fire hazard. A heat gun on high will do this too unless you are very, very careful.

Fire hazard? What burns - the canvas? I took a couple minutes to check MSDS on Golden's site (file:///C:/Users/Michael/Downloads/msds-all-golden-products%20(1).pdf) and they all show there is no flash point or other flammable limits (LEL or UEL), so it's a good bet these paints, at least those that come out of tubes, don't burn. They will melt, though, and when they do they give off toxic gasses.

Good information about the pin holes when over heated. :thumbsup:

R/Mike

Davkin
06-11-2015, 09:27 AM
Ya, I wouldn't think acrylic paint would be very flammable, if anything caught fire it would be the substrate. A hair dryer will work without any real danger since they don't get as hot as a heat gun. I've heard of people putting their paintings in an oven but I'd think you'd have to keep the heat relatively low to not risk damage, it's more about chasing away humidity than heating the paint up anyway.

Mike L
06-11-2015, 11:19 AM
This might be the definitive answer. Well, maybe the best rule of thumb so far voiced. :lol: It isn't a specific time frame, but it is a very specific set of conditions that will indicate whether or not a painting is cured enough for varnish or other coatings.

Golden recommends waiting to varnish (http://www.goldenpaints.com/technicalinfo_drying) until the paint is cool to the touch. Moisture in the paint continues to evaporate until, essentially, all the moisture is gone or it reaches equilibrium. (it's a bit more complex than that, but the result is simple to understand. It is the same principal that is believed to have been one of the contributing causes of the sinking of the USS Thresher in 1963) Much of the moisture evaporates through the paint skin, although some does wick through the substrate. When the skin of the paint is cooler than the surrounding air, the paint is still curing.

When moisture in the paint evaporates, it cools the surface of the paint, hence the painting is still curing if it is cooler than the surrounding air. This is the same principal the human body uses to carry off heat - sweating. As long as you sweat the surface of your skin will be cooler than the surrounding air because the evaporating persperation is carrying off the heat.

It isn't a big difference; maybe only a degree or two, but using the backs of your fingers between knuckles and second joint up will let you notice the difference. When the skin of the paint is the same temperature (by touch) as the air, it should be OK to varnish. How long will that take? As already pointed out, the time frame is dependent upon several factors -air temp, humidity, what's in the paint (think brand specific recipes) how thick it is, and even the colors chosen.
To verify my theory I performed the following test:


Placed a painting with thick paint beside one with thinner paint. Both of these were completed in the last two days.
A third painting, completed in April was added to the mix.
The group sat for ten minutes so they could acclimatize to the same place in the room. The older painting was in direct line of the air conditioning air flow so was as cool as that temperature. Paintings rested in a spot not exposed to air flow.


Results - Thick paint noticeably cooler than the thin paint. Older paint noticeably warmer than the new two. Try it, you might be surprised.


R/Mike

Davkin
06-11-2015, 12:32 PM
Your skin is a very poor thermometer. I wouldn't rely on touch to tell me if a painting is cured, our senses fool us all the time. Maybe an infrared thermometer would be accurate enough.

Mike L
06-11-2015, 01:09 PM
Your skin is a very poor thermometer. I wouldn't rely on touch to tell me if a painting is cured, our senses fool us all the time. Maybe an infrared thermometer would be accurate enough.

My post was meant to tell you how to do determine if your paint is cured. All I've done is pass on what paint manufacturers say on the issue. I've offered a logical and scientifically (check out Bernoulli's equations that describe what happens to a gas as it passes through a nozzle. Newton also did some work in this area.) backed explanation as to why it works and then offered a simple method to test it in your own home or studio.

Skin is not a thermometer in any sense of the word. Unless trained to recognize a specific temperature, skin will never inform the brain what the temperature is of the item being tested. To think of the method described as such is probably quite a leap of logic. Besides, the accurate and precise temperature is immaterial, I think, because we are looking for a difference in temperatures, not quantifiable measurements.

The nerves beneath skin in many areas of the human body, are, however excellent means for determining if something is hot or cold (go ahead, grab the end of a burning match) and finding out if the temperature of one item is different from the temperature of a similar item in the same environment. It is such a good means of determining whether something is too warm or too cold that the method has been used ever since bottle feeding of infants was invented. The nerves have to recognize the differences in temperature to know if something is too warm or too cool.

If you like using an infrared thermometer, by all means, please do. Perhaps you'd share your experiences with that method?

It is not my place nor was it my intention, by any means of the imagination, to tell you or anybody else how they should determine if their paintings are properly cured. Besides being sensible, if this method is good enough for a respected paint manufacture (http://www.goldenpaints.com/technicalinfo_drying)to recommend it, it is good enough for me until I gain many more years experience or someone offers a better way.

R/Mike

PS Before posting this I dug out my infrared thermometer. The temperatures for all three paintings is 72.3 degrees (F).

Davkin
06-11-2015, 03:20 PM
You're talking a couple degrees difference, between ambient temp and a surface temp no less, nobody's skin is that sensitive. Even when talking relative temperatures our senses are easily fooled. Sorry, but this is no kind of test at all, it's meaningless unless you use a more reliable instrument than your finger.

Mike L
06-11-2015, 04:04 PM
You're talking a couple degrees difference, between ambient temp and a surface temp no less, nobody's skin is that sensitive. Even when talking relative temperatures our senses are easily fooled. Sorry, but this is no kind of test at all, it's meaningless unless you use a more reliable instrument than your finger.

Maybe less than that in some instances. To you it's meaningless, and I won't begrudge you your opinion. The method does not 'take a temperature' it simply indicates a difference between two values, neither of which has any bearing on the issue beyond being different one from the other. If you can't tell there's a difference, you can't tell there's a difference, and that is not a sin. My skin is that sensitive on the backs of my fingers, insides of my wrists, area between my upper lip and bottom of my nose. My ears are pretty big, so it's possible they are reliable heat sinks, too. :lol:

I think a whole lot more folks also have skin/nerves sensitive enough to tell the difference. If not, I doubt paint manufactures, who know a lot more about it than you or I, would recommend the method. They have already used the instruments and mathematics and chemistry and whatever else to study the variety of phenomena their paints exhibit.

Do you know of another technique that is easier, reliable for 100% of the population, and less expensive? I'd be glad to hear it, even put it into use. Until then I won't comment on any more of your posts to this thread. You have your opinion about the information I presented and you're welcome to it. But, please, don't poke the things you don't like just because you don't like them. (They might poke back :lol: :lol: )

R/Mike

Davkin
06-11-2015, 04:28 PM
Set of piece of wood and a piece of metal on your desk. Let them sit there a while to be sure they assume room temperature. Now touch each one. The metal will always feel cooler than the wood even though they are the same exact temperature. (I'll let you look up why that is) This is just one example of many how our senses fool us all the time.

It doesn't matter how inexpensive or accessible a method for measurement is if it's unreliable.

Mike L
06-12-2015, 10:19 PM
I know I said I wouldn't respond, but comparing wood and metal to acrylic paint is beyond the pale. That is not the topic of the thread. Stop for just a minute and think - Take a minute to read Golden's technical recommendation on the issue of determining when a painting has cured. Please. You've been offered the link several times. Or don't - that's OK.

If you disagree with the people that know more than I do on it, that's OK. If you disagree with the people that know more than you do about it, that's OK, too. If you don't want to use the method the professionals recommend, that's OK, too. What ever you do with the information is quite alright. You won't be arrested and your AARP membership won't be rescinded. (I hope :lol: )

I'm not a scientist, but during 21 years in the US Navy I was a marine propulsion engineer and specialized in gas turbine (jet engine) propulsion for surface ships. I know quite a bit about heat, heat transfer, and engineering principles. In short, I'm fairly well trained and experienced so I can recognize theories that are sensible as well as ideas that are meaningless.

So, yes, I already know why different materials seem (and sometimes actually do) exhibit different behaviors in the same environment.

I am unsubscribing from my own thread, so feel free to have the last word.

R/Mike