dinsdag 17 maart 2009

Warm gesso recipe

Hm, some of the notes from last week were not saved, notably, the plans we made for this week. Also we're distracted by dance plans after we attended the wonderful Accademia della danza this weekend. When we finally tried to start a batch of gesso we realized we should have set the hide glue to soak for two hours, and it's too late to start that now, so we'll make some orange paint and practice writing.

Eureka! Totally accidentaly the orange batch makes a pretty nice red that might work for the dragons. Made by adding 1 part of kraplak to 4 parts of ercolano orange. 1/10th kraplak added to ercolano orange still seems a bit too red for the color used in the Rijmbijbel. All of this with gum arabic as the binder. The paints are a little transparent, so in the next batch we'll try to add a bit of marble dust to make it more opaque.

What we can remember from last weeks results is:
-the new burnisher works better for small bits, for larger surfaces the stone works just as well.
-the loose gold does not cover the gesso better than the transfer gold, but it is really annoying to work with!

Plans for next time:
-make warm gesso and use on book
-start writing text in the book
-oranje/rood verven marmerslijp erbij vanwege dekendheid

The recipe from Randy Asplund is this:
Gold is stuck onto the page by laying it on a thick ground called gesso (see fig. 6). I used a gesso recipe based on one which dates from the anonymous Naples MS XII.E.27, known as De Arte Illuminandi. It dates from the end of the 14th c., which makes it later than the style I am emulating, and from a different region, but since the gilding recipe is very simple, and there were so many different recipes, I felt that itís use was justified. This recipe contains hide glue which has been pre melted into water at a 1 part glue to 14 parts water ratio, some dry powdered Armenian Bole, some honey, and some slaked plaster of paris.
I began with a double boiler which I used to melt the hide glue. You never want to boil hide glue, and you reheat it as few times as possible, or it loses adhesiveness. I can store the melted hide glue for a very long time in an airtight jar in the refrigerator. It will keep as a gelatin. I also use the double boiler to warm some honey to the point where it will flow in an eye dropper.
I pre-mix and slab grind 4 parts of slaked plaster with one part of a soft clay called Armenian Bole and store that in another 35mm film jar. It is important to grind on a slab rather than in a mortar because a pestle will not reduce everything to a uniform fineness. Instead of slaked plaster one may use calcium sulphate (CaSO4), chalk, sea shells, egg shells, or even fine marble dust. If you use plaster (which is roasted gypsum dust) it must be slaked or it will not be inert. Slaking is when you add a lot of water to the plaster and agitate it until the plaster has stopped combining wit the water molecules. Then it canít form a structure anymore.
For this recipe I dumped a half tsp. of the pre-mixed plaster/bole into a small ceramic mortar with an equal amount of fluid, melted glue. Then I started by adding ten drops of honey, and ground the material until smooth. The honey makes the resulting gesso slightly flexible, and it allows it to become moist again when breathed upon.
The real trick is to put in just enough honey to make the gesso become slightly tacky when you apply a long, slow, moist breath, but to also be totally dry otherwise. If it doesnít dry completely, you canít burnish it later, and it will smear. The color of the gesso changes from dry to wet. The light dry color will never reveal itself if there is too much honey. It will always be dark from an overabundance of the honeyís dampness. I painted out a test and found I needed more honey, so I added two more drops, tested again, and added one more. The gesso was then painted on in two layers with a brush. It was mounded only high enough to rise above the surface texture of the page. I should have sanded or scraped it smooth after it dried, but it seemed smooth enough, so I skipped that step.

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