Wednesday, May 25, 2016

Making Traditional Gessoed Panels

 For this project, I decided to make panels with traditional preparation methods and gesso.  I chose poplar panels as this was a common wood used for panels in period, particularly in southern Europe.

 Step 1: Glue Preparation - I heated rabbitskin glue (RSG) and water in a double boiler according to directions on the package.  A couple of coats of this was brushed on to all surfaces of the panels. 

Heating the rabbitskin glue in a double boiler.


Sizing poplar panels with rabbitskin glue.

  Step 2: Applying the Linen - prior to gluing, I had cut linen to the approximate sizes of each panel.  The linen was soaked in the RSG and smoothed over the panels, removing any air bubbles.  I also brushed on an extra coat of RSG atop the linen.  The extra RSG was put into a container in the refrigerator for use in later steps. These panels were allowed to dry for a couple of days.

Applying linen soaked in RSG to the panels.

The dried linen glued to the panels and trimmed.

 Step 3: Slaking Plaster:  1 part plaster of Paris was combined with 4 parts water in a bowl.  A lot of this was needed  for the gesso process so I prepared 5 cups plaster to 5 quarts water.  This is then stirred well and allowed to settle until a layer of water forms on the top.  This is poured off and the process is repeated a few times.  PH strips are used to test acidity - the slaked plaster should test as neutral to be considered done.  The plaster is scooped into a rag, the excess water is squeezed out, and these can be formed into loaves.


Loaves of slaked plaster.

Step 4: Preparing the Gesso - Some of the refrigerated RSG was  reheated in the double boiler, and a couple loaves of slaked plaster was crumbled into it, and whiting (I used titanium dioxide; lead white would have been used in period) was added.  This was mixed well to remove lumps.  I applied one coat to the back of the boards and 8 coats to the front, allowing the coats to mostly dry in between.  This is a long process, and the time between coats gets longer towards the end, as it takes longer to dry; however Cennini recommends to keep going with the process until done.  Keep the gesso mixture on low heat throughout, adding more water, RSG, and plaster as needed.  The extensive coating process is needed, though, as the boards will be scraped smooth later.  These boards should be allowed to dry for at least 2 days after.

8 coats of the gesso mixture applied to the panels.

 Step 5: Scraping the Panels - Wood boards will naturally curve, and after gessoing they will most likely be slightly convex.  However, in looking at panels at museums, many boards are shaped like this and it can be seen that they were like this prior to painting, as there is no cracking to the painted surface that would be expected.  Moreover, often a curvature was provided on the inside border of the frames to accommodate this deformation.
Vine charcoal was ground in a mortar and tied into a rag.  This was pounced over the surface of the panel and a feather was used to spread out the dust. I obtained a long flat scraper from the hardware store and used this, scraping over the entire surface of the panel until all of the charcoal was gone and only white gesso remained.  I sanded the final board with 400 grit sandpaper, for a smooth ivory surface.

The dried panel pounced with charcoal and ready for scraping.

The scraped and sanded panel, ready for painting.

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