Posted by Raymond Chapman on April 16, 2003
Lee LittlewoodThis is not meant to be a smart-aleck question, but something that I wondered about.
Since glue chipping relies upon removing moisture from the glue and this is more effective in low humidity areas than those near the coast, how does raising the temperature (as in a booth) speed up the process? In Houston when the temperature is 105 it is not any drier than when it is 40. It seems that heat or cold would have no effect on the drying process since lower humidity is what is needed.
Just one of those things that make me go hhhmmmmmmm!
One other way of helping the glue chip process along is to put the glass in an air tight container (like a plastic garbage bag) and adding silica gel desiccant. It is the stuff that is used to dry flowers and also what is in you camera or other electronic equipment to keep the moisture out. It always says "Do Not Eat". Who would be tempted to eat the stuff, anyway?
Raymond ChapmanA good analogy is a sugarcube at the bottom of a glass of tea. You can make it dissolve faster by heating up the tea OR by stirring the tea. Stirring is the "relative humidity" and heating is, well, the hot air. I'm not sure what using dessicants is like; maybe like sipping some of the sweetened tea and replacing it with unsweetened tea again and again. Maybe it's not a good analogy.
Another way of looking at it is from the point of view of the water molecules. Now, EVERYTHING wants to "get equal" - mountains wear down and lakes silt up, wet paint smell travels all through the shop overnight, a drop of ink in a glass of clear water will make an even (though light) tinted color. (This is the Second Law of Thermodynamics: entropy tends to increase to a maximum. Entropy is a measure of disorder. As signpainters we are very familiar with increasing disorder, just look at our desks.) The water wants to get out of the glue until it is equally outside and inside the glue. Left alone it will get equal, but so slowly that the glue would probably not shrink enough to pull chips off of the glass, so we have to speed it up. I'm not sure if it is possible to speed it up too much, and make a hard skin form on top of the glue which could keep it from contracting and chipping glass. Has anybody had that happen?
CarolWow, Lee, that sounds like I'm listening to Rick. I don't know if all that stuff is true or you're just pulling my leg. But it sure sounds good.
It makes sense that the moisture inside the glue is trying to balance with the moisture outside the glue (in the air). Thus, the process is quicker in those areas with a dry climate. I guess heating the process speeds up the movement of the water molecules and makes the whole process go more quickly. Just like that old man Doug's analogy of the pan of water on the stove.
Sounds simple now. Thanks for straightening me out. Even you, Doug...Thanks.
Vance GalliherSorry if I'm telling you something you already know, but It's relative humidity. Relative to the amount of moisture the atmosphere is capable of holding. It is capable of holding more at higher temps.So if your temp is 40 and humidity is 40 and you raise the temp to 80 the amount of moisture in the air remains at what it was at 40, drops the percentage. That's why in cold climates you have to add humidity to inside (warmed) air or your skin dries out. That's why Vance's drying box works.
ok ok you already knew all that.
Mike Jacksonhi raymond......living in oregon,i have used the black bag/silica/small heat fan combo many, many times........it does work, but up here it takes sometimes days to chip.........that's why i built the hot box....vance
Raymond ChapmanHi Raymond,
Part of your dilemma is you are from Texas!(Texas jokes implied and intended). In Rick’s case, living not too far from the ocean, he had humidity but it was combined with 85 degree summer days. At 105 degrees in the summer on average, I can see your concern. Apparently the heat produced by the lamps dries out the air in the enclosed area. Next door to us when we had the shop in Oklahoma (go ahead, apply the jokes), there was an company that made mobile oil field testing units. Part of their testing units used silica crystals to remove water and humidity from the samples they were taking. The silica crystals also had some colored indicators mixed in. When the indicators were blue, the material was ready to absorb water, but if pink, it had lost its ability to absorb more humidity. Right? There’s a point here somewhere... Well, as I said, that was in equally humid Oklahoma. To dry out their silica crystals, they poured it out on a table top with a heat lamp directly over it. By the next morning, the indicator crystals were blue.
So, to answer your question, "It just does".
Mike
D. Bernhardt - Dummy Up Ray!Thanks for that lengthy way of beating around the bush.
"It just does". It's easy to see that you are a parent. That answer falls in there with "Because I said so."
I know that the crystals can be reused once they have absorbed moisture because the cannister that I have says that they can be put on a cookie sheet and dried in the oven.
I guess the heat drives out the moisture somehow. By that reasoning, though, it should just get drier in Texas in the summer as they heat goes up. Maybe the humidity in the air is coming from the moisture being driven out of the soil, creeks, etc. That my story and I'm stickin' to it.
Thanks for the attempt, anyways Jackson.
Raymond Chapmanso if youre so smart how come if you but water on a hot plate it evaporates pronto...if the plate is cold....it takes forever...huh! ;=)
How do you "but water"? Must be a Canadian term.
OK, OK...it just does...alright?
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