RSG Gesso

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GeoSpectrum
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RSG Gesso

Post by GeoSpectrum »

I’m making up some RSG gesso for the first time. I’ve soaked the RSG overnight and am going to warm it on a double boiler. The bit that’s eluding me is the ratio of RSG to whiting? This is for a painting surface not a frame if that makes a difference? Thanks
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Re: RSG Gesso

Post by vintage frames »

Hi GeoSpectrum. It's actually the ratio of RSG to water you need to think about!
No matter - the ideal weight to volume is 30gm RSG to 500ml water. If you know to what proportions you've already soaked, then you can add more water to make up the difference if necessary.
Then, for gilding I use a 1:1 ratio RSG to whiting. If you're spraying, then two coats of that mix will do the job. Adding more whiting will thicken the mix at the expense of it being a bit more friable and difficult to spray; adding more RSG will make a harder gesso that's difficult to sand.
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Re: RSG Gesso

Post by GeoSpectrum »

Ok, thanks, I’ve mixed 1part RSG to 12 part water? I see 800mlnof water so I recon that was 66 grams of RSG. So I should get just over a litre?
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Re: RSG Gesso

Post by vintage frames »

Yes, I think that's right. I can never get my head around the one part solid to one part liquid ratios. Weight to volume is more straight forward. Anyway it's the glue strength that determines everything else.
You'll find the liquid gesso slightly translucent compared to paint but it dries very opaque. Spray it hot and clean out with boiling water.
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Re: RSG Gesso

Post by Bertie »

I've recently started sanding my gesso with mesh sanding discs, which are a revelation compared to your standard sandpaper as they don't clog.
Perhaps this is old hat to framers who use gesso... does anyone else use them for this? As you rotate them whilst sanding, the dust just falls away...

I have a Mirka disc sander for furniture making (although I have been known to use it on flat parts of gesso frames!) and use these discs:
https://www.ebay.co.uk/itm/Mirka-Autone ... 2727029583

The Abranet discs are meant for wood etc but I honestly can't tell the difference between these and the Autonet, besides the cost. One disc easily does a large frame too.

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Re: RSG Gesso

Post by GeoSpectrum »

Fist coat done. How long to leave it between coats. It’s on a flat panel, it hasn’t gone on particularly smooth but I guess sanding will sort that?
45706940-CEB9-4BB5-843D-367447396AC9.jpeg
Alan Huntley
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Re: RSG Gesso

Post by vintage frames »

You can spray over that as it cools. The surface goes a bit matt as this happens. It's a case of little and often. Too close and too early can blow the wet gesso off! Just spray from a little more distance as you build up the surface. Gets easier once you get used to it.
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Re: RSG Gesso

Post by GeoSpectrum »

Thanks. It’s sticky at the moment so time for another coat. How long to dry hard?
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Re: RSG Gesso

Post by vintage frames »

I've got a pneumatic disc sander and use the standard discs from Mirka, because of a large remaining stock but I'll be trying the mesh ones soon. You're right in that the standards clog up quickly. Whats more important is using the right grits. Also wearing a pair of blue vinyl gloves to protect your fingertips.
I wouldn't be using the sander on gesso though!
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Re: RSG Gesso

Post by vintage frames »

Overnight - in summer. If it's a really thick layer, then 48 hours.
I don't spray large panels like that, only frames, but when its all dry you could wipe over the surface with a wet sponge to flatten things out a bit and save some effort on the sanding. The water from the sponge will be quickly absorbed and evaporate.
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Re: RSG Gesso

Post by GeoSpectrum »

Thanks. I if I get the order I’ll probably be splashing out on a Mirka sander, I have my eyes on them for a while but £300 is a bit steep for normal sanding. I’m hoping the panels will be a regular order. If anyone’s interested they are made of the 25mm ally subframe from Lion and an outer of F9 from Rose and Hollis with a dibond panel bonded to it and trimmed with a trim router. They are quite expensive for the customer but they wanted a very rigid panel as they are going to be mostly 1200x1000.
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Re: RSG Gesso

Post by vintage frames »

You were saying that you'd priced a sander at £300. Whilst I was looking at the e-bay post mentioned by Bertie, I noticed a Sia sander with 20 boxes of discs for £189. That's the sander I have and it's still going strong after 25years! It is pneumatic however and does drink a lot of air.
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Re: RSG Gesso

Post by GeoSpectrum »

Thanks for the tip on the sander.

The gesso was not a success. It just stayed sticky and scraped off easily. I must have got the recipe wrong by a good margin. I’ll try again....
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Re: RSG Gesso

Post by vintage frames »

Sorry to hear the first attempts didn't work out. Whatever reason aside I'll put up here the procedure I would follow if that was my project.
Soak 40gm of RSG in 660ml water for 4 -5 hours or overnight.
Heat up to melt no higher than 70C, DO NOT BOIL.
Decant 400ml aside and pour the rest into a yogurt pot or other.
Pour the 400ml back into the empty saucepan and add in 400gm of whiting.
Stir this around for at least 1min, but don't whip. I like to add 2 teaspoons of brandy as this helps reduce surface tension.
You can use this gesso now but it actually improves if set aside for several hours.
After bringing the gesso back up to heat, 70c, brush 2 coats onto the panel. Use a natural bristle brush for this. This helps prime the surface and works away any oily or greasy patches. Leave that to set for 20min or so.
Now fill the spraygun with the hot gesso through a seive. Spray on one even coat.
Let the gesso cool a bit and go matt on the panel.
Now spray on a second coat and if you hold the gun well back you can build up the surface a little more.
You're done. Leave it to set for at least 24hours or more if the weather is cold.
I hope this can be of some use.
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Re: RSG Gesso

Post by GeoSpectrum »

Many thanks. That's my task for the weekend.
Alan Huntley
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