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MDurante
09-28-2004, 06:38 PM
Oh no!

To increase working time, I sealed my acrylic-gessoed surface with gloss acrylic medium. This gave me a nice smooth non-absorbent surface. With the aid of glazing liquid and a spray-bottle, I could keep working the paint to my heart's desire. It was really quite wonderful. And if I made an uncorrectable mistake, I could wipe the whole layer off and it would be gone completely!

"Slick," I thought. :cool:

But then it happened: I wiped too hard, and started to remove layers beneath -- all the way down the the clear medium! The lowest layer had been drying for a day...

NO!!!!!!!

Am I totally neglecting the adhesive requirements of acrylic paints? Do others work in this way? It has many nice properties and I'm going to keep trying.

But will my painting eventually fall off? :confused:

My next experiment will be to seal each layer or "glaze" with another layer of clear gloss medium. Hopefully that will work.

Thanks for any insights,

- Matthew Durante

Bertoni
09-28-2004, 06:48 PM
WOW! I can't wait to hear the solution to this problem myself! Hopefully someone here will come up with an answer??????

Alena Hope
09-28-2004, 06:51 PM
I guess I must have missed something in what you are saying because even the acrylic mediums (with the exception of a retarder) dry relativly quickly even when used on their own. So, you started with a gessoed surface and on top of that you put the gloss acrylic medium. I'm wondering why....maybe try drying your layers when your done with a blow dryer to speed it up so it doesn't happen again. I know if I get too overzealous with the paint it takes sometimes two days to dry completely. An example is the octopus I'm working on now, I have been using the hard molding paste to create 3-d tenticles and suckers and the paste takes at least a day to dry each layer and I'm really building the layers up so I'm on layer #3 and I can tell by how cold the paste feels that the layers under it arn't 100% dry. My solution...the blowdryer...makes my hair look terrific and aides in drying time on acrylics...taaaaaahhhh daaaaahhhhh!

MDurante
09-28-2004, 07:13 PM
Alena,

I put medium over the gesso so that it wouldn't absorb water from the paint, making the paint dry slower. My goal is to extend drying time as much as possible. By doing this, I only (perhaps) have to worry about evaporation of water from the paint, and by adding water at intervals with the spray-mister I can account for that somewhat.

I'm not a chemist, but my understanding is that drying time of acrylics is determined by absorbtion and evaportion of the water from them (which can of course be effected by temporature and humidity, etc.).

Please people correct me if I'm wrong...

Hope that makes sense,

- Matthew Durante

Mike Finn
09-28-2004, 07:49 PM
Matthew..

If you use any sort of retarder, and I "think" glazing medium has a retarder, then you must let each layer dry for longer than a day if you use too much. Three days may be ok. If the retarder has not completely evapourated then the next layer will reactivate it and it will wipe off..... found that out in hurry :-) The recommendation is less than 10% but even that requires a good long drying time.

Mike Finn

MDurante
09-28-2004, 09:05 PM
Thanks Mike,

It definitely could be the retarder, and I've seen that happen before (I think Golden's Glazing Liq. is 10-15% retarder).

It just lifted so easily this time and so completely that I thought it might be weak adhesion to the layer of medium.

I wonder if it is safe to isolate retarder-filled layers with medium before they are completely dry (but dry to the touch)?

- Matthew Durante

Andrew
09-28-2004, 09:12 PM
You may have done too good a job at sealing the gessoed surface. It may have been to slick, and the paint wouldn't adhere. Just a guess, without actually being able to examine the evidence.

Andrew

John H
09-28-2004, 10:06 PM
It's my understanding that when acrylics dry, just the top skin dries fast. What's under the skin stays wet longer. I've rubbed too hard before when adding additional coats of paint and taken the paint down to the gessoed canvas. I was just using paint and small amounts of water (no mediums). So maybe just a lighter touch is the answer. Not sure.

Mike Finn
09-28-2004, 10:09 PM
Thanks Mike,

I wonder if it is safe to isolate retarder-filled layers with medium before they are completely dry (but dry to the touch)?

- Matthew Durante

Matthew...

I know Atelier and most probably everyone else, makes something called "Retouch Varnish" They recommend using this for just that purpose, sealing reworkable layers. You might investigate that.

Mike Finn

MDurante
09-28-2004, 11:15 PM
Thanks everybody for the good info!

It looks like I'll have to test to determine whether it was too slick of a surface or simply non-dried paint. All I can say for certain is that I liked painting the initial layers atop dried medium rather than gesso, because I could work the paint much longer.

Newbie question: it's the chalk in gesso that accounts for its absorbency, right? Dried acrylic paint does not have this property? :o

I've heard of retouch varnish but never used it. I imagine the advantage to it rather than medium is that it can be sprayed, so you don't have to worry about brushstrokes. I'll have to look into it...

Thanks again,

- Matthew Durante

Einion
09-29-2004, 11:28 AM
Hi Matthew, Golden have some good recommendations on how you can keep working wet (on canvas) on their website which you might like to have a look at. If that's not quite what you'd like may I suggest painting on hardboard/ply/MDF sealed with polyurethane prior to applying the acrylic primer. That should take care of the bulk of the absorption from the ground. You might also consider melamine-surfaced boards, properly abraded to ensure good adhesion and perhaps primed first with a thin layer of automotive primer or Kilz.

It just lifted so easily this time and so completely that I thought it might be weak adhesion to the layer of medium.
That sounds very likely.

I wonder if it is safe to isolate retarder-filled layers with medium before they are completely dry (but dry to the touch)?
I wouldn't, see below.


It's my understanding that when acrylics dry, just the top skin dries fast. What's under the skin stays wet longer.
That's basically correct John. Acrylics dry by evaporation mostly as we know and the evaporation has to occur out to the air so you get a dryer skin while the paint underneath is not completely dry - you can see this if you've ever left a pile of paint on the palette that's hard and rubbery and found that there's a small pea of useable paint inside it.

This is why reliable guides to acrylics warn about letting the painting dry for longer than a couple of hours if you've painted thickly before you can consider the painting actually dry. In very thick applications of acrylic paint it's possible for the paint to take months to dry properly apparently.

Einion

MDurante
09-29-2004, 02:39 PM
Thanks Einion for the suggestions.

Here's Golden's article on drying if anyone else is interested: http://www.goldenpaints.com/technicaldata/drying.php

As for locking in non-dry layers with medium, I guess since the medium is probably not porous the layer below would never dry (especially if it is samwiched between two layers of medium). Hmmm... I'm still going to experiment but it's starting to sound like a bad idea...

I'm starting to understand why many people use water alone, without retarder. If one has to wait days just to be safe that thin lower layers are dry so they won't lift, suddenly acrylic painting becomes more like oil painting.

Oh wait -- hairdryer!!! :evil:

- Matthew Durante

Einion
09-29-2004, 04:55 PM
As for locking in non-dry layers with medium, I guess since the medium is probably not porous the layer below would never dry..
Acrylic paint or medium is actually quite porous, it's just that it will slow the process down further which I thought would just make your problem worse :)

I'm starting to understand why many people use water alone, without retarder.
That's me!

Einion