Is there a satisfactory substitute for the (highly toxic) lead in raised gesso recipes other than titanium, which I understand produces inferior working characteristics? If there is another way to do burnished raised gilding on paper or vellum, I would be very eager to hear about it.
I do not think there is a good substitute for lead white, because it provides some excellent properties in addition to a white pigment. Zinc oxide may be the best substitute if you are trying to avoid lead in raised gesso recipes.
I've found other recipes for raised gesso on the cennini21 website and they have no lead at all -- and some have a higher proportion of bole. I wonder if extra bole would work? I'm assuming the lead primarily provides ductility, but I've read varied accounts of what the lead supposedly provides beyond ductility including flexibility, fungicidal action, filling in holes in the plaster, strength. Is bole liable to crack on a thick gessoed paper base?
All of these substances, bole (which is a clay), chalk and gypsum, are liable to crack because with collagen glue they form an inflexible ground. Lead provides some of the qualities you wrote about, but not to any significant degree. It mostly provides opacity and the ability to take a good polish.
May 12, 2010, 10:18 AM
Which type of animal skin glue (tests have reputedly shown it to be superior to fish glue) would be best for a raised gilding gesso formula? Genuine rabbit skin, Italian rabbit skin, rabbit skin, hide glue, gelatin? I'm suffering from a case of overchoice.
May 12, 2010, 10:26 AM
in order of choice, from my understanding.. Italian rabbit skin glue, genuine rabbit skin glue, rabbit skin, hide glue, gelatin would be the better choices for raised gilding in that order. Most of these are at least from my understanding preferential to common fish glue. Isinglass is a different ballgame all together.. In that it is a higher strength glue than all the above, but much much more expensive.
George will of course provide the authoritative answer though.
May 12, 2010, 10:35 AM
The choice of collagen glue depends on your requirements. Most gilders use collagen glues with lower bloom or gel strength, because these glues have longer open time and set to a softer gel, which is important when burnishing the glue to a high polish.
In order of bloom strength, the highest to lowest among the collagen glues offered by Natural Pigments are genuine rabbit skin glue, rabbit skin glue (domestic), Italian rabbit skin glue, hide glue (domestic) and technical gelatin (domestic). We will soon be offering fish glue, which will also be a good choice for gilding, with an adhesive (not bloom) strength comparable to that of the best animal glue.
Robgar is basically correct in his assessment of Isinglass or genuine sturgeon bladder. However, it is so expensive that few gilders use it.
That said, the preference among professional gilders appears to be somewhat arbitrary, because many gilders in Europe prefer Italian rabbit skin glue, whereas here in the U.S., it ranges from rabbit skin glue and hide glue to technical gelatin.
[ 12. May 2010, 21:23: Message edited by: Admin ]
May 12, 2010, 12:06 PM
Isinglass (or at least something called that) is used in brewing beer, for clarifying the brew. It is a powder rather than a bit of flesh and is relatively cheap. Is this the same thing?
Also, are any of the choices able to be used at room temperature rather than having to be gently heated?
Thank you both so much, by the way! This forum is a marvelous place.
May 12, 2010, 01:30 PM
Whereas a type of isinglass is used to clarify sumptuous beverages, such as beer, it is made from cod and does not have the same properties as genuine isinglass from Beluga sturgeon swim bladders, which commerce is fiercely controlled by the Russian government, and hence quite pricey.
Now for some Beluga caviar with my Beluga bladders.
Fish glue can be used at room temperatures, and this is another reason why some gilders prefer it, although rarely employ it.
[ 12. May 2010, 21:21: Message edited by: Admin ]
May 12, 2010, 02:53 PM
If I understand it right, robgar indicates that isinglass is very strong, hence it would have a high bloom, correct? In which case it would not be as desirable as a gilder's glue because it would set up harder and faster and thus not take a good burnish, right? I've never heard of anyone using isinglass in gilding for illuminating manuscripts except in conservation and restoration, so I'm just curious.