Gesso - too many bubbles!

[Coxby]

As a young paduan in the art of making gesso, I am finding too many air bubbles appearing when it starts to dry on the moulding! I have been reading McTaggarts Guide to Gilding and am aware that too much stirring can cause this. I kept stirring to a minimum but had to do some otherwise my gesso would take on the same texture as my old school's food

Does anyone have any nifty tips on how to achieve a lovely finsih that doesn't resemble an Aero bar!!*?£!!

[JFeig]

I can think of 2 reasons for bubbles in gesso. 1. a dry base and too much brushing. 2. a poor gesso formula.

When I gesso a frame I first apply a thin coat of RGS (rabbit skin glue) at base strength. 16 gm RSG to 180ml pure water. This will vary silghtly with the time of the year and the humidity.
My first coat is applied rather liberally followed by smooth thinner coats. 5-6 coats in total. I use a good quality 1" (25mm) squirrel flat brush (about $8.00 ea.). Also do not overheat the gesso or glue. The hotter it is the weaker the glue will be. The heat will reduce the length of the molecue and this reduce the strength. In the US 125-135°F as a max. Overbrushing the layers can also cause bubbles. Your gesso will thicken as it is in a double boiler. Additional water can be added as necessary. I will sometimes smooth out a tip layer of gesso with a brush dipped into my double boiler's water (no or little gesso in brush). Each layer of gesso is applied over a semi dried priorr layer (the gesso is not completely dry;it is whitter that when wet). Sanding is done after the gesso is completely dry. I store im base gesso in a refrigerator (2 weeks) The gesso placed in a double boiler for actual work is not placed back into my stock. It is thrown out.


Gesso formula
8 parts whitting - by volumn
2 parts filtered water
4 part stock RGS

mix warm in double boiler and store in a sealed glass jar in refrigerator. Reheat or keep warm only what you will be using for your job.


Jerry

[JFeig]

I forgot to add.....

If you have any more questions, let me know

member Society of Gilders since 1988 and former board member

http://www.societyofgilders.org

[Coxby]

Hi Jerry, I been following your instructions to the T but I have a couple of problems still occuring. The first one is that the squirrel brush I am using tends to hold on to the gesso too much and I find I have to slap the gesso on to get any result, hence more bubbles. The problem with this is a) it takes too long to get a consistent layer over the whole frame and b) depth isn't consistent especially around mitres. Maybe my Gesso is too thick, but I mixed to your guidlines exactly, but when you say 'by volumn' what does that mean, 8 parts whitting - by volumn 2 parts filtered water 4 part stock RGS. The gilding course I attended suggested the gesso should be a blood temp, but you say 125-135°F as a max. Is there a DVD out there to help me visualize the technique? Thank you in advance.

[SquareFrames]

Hi Coxby,

Not having ever done gilding, I have no use for it, as yet, but I suggest contacting - Pierre Lafrance, 15 Pinewood Avenue, Northbourne, Bournemouth, Dorset, Tel: 01202 582957. Pierre is one of the UK's most repected Gilders and holds courses, etc.

Good Luck.

Steven