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16th. Century Venetian gilded tabernacle frame with hand cut and carved mouldings.

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Adam W.

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Thanks.

Here's the what the frieze panels look like just before sanding, they feel robust, but really they just want to fall apart if you look at them the wrong way.

I scraped it flat on the back when it was still in the mould, as they snap if flexed and the mould is fairly deep and quite thick in parts. Then I laid it on a sheet of glass so that I could apply downwards pressure to make the mould flex so I can get it off.

I sanded it down to make it as flat and thin as possible and I broke three before I got one out and I broke the fourth when I was glueing it down, but it didn't move apart and all the coats of rabbit skin glue and gesso which come later will hold it all together.


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This is how the originals were made in 1500, so I'm on the right track.

This one is in the workshop at the National gallery in London and the cast is very thin considering the amount of modelling it has. Theirs was cast in much smaller sections all joined together to form the full width of the frieze.

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dzj

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Very interesting!
How did they make the mould back in 1500s? Perhaps some kind of clay?
 

Cooper

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How did they make the mould back in 1500s? Perhaps some kind of clay?
Surely they would have carved a pattern on thicker wood and then made a mould from gelatin.

I'm interested that Adam is achieving such delicate carving from pine, with such an open grain. I had presumed that all the fiddly bits would be from Lime.

Its so interesting to see the production techniques so clearly.
Keep up the good work!
 

Adam W.

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Very interesting!
How did they make the mould back in 1500s? Perhaps some kind of clay?
I think they modelled it in clay, as it's quicker than carving one and the mould was made of gelatin and wax. The original ones all look like they've been modelled rather than carved and the Venetians were experts at applied stucco at the time.

Larger applied ornaments for buildings were first modelled in lime and hair plaster and covered with a coating of gypsum plaster, so the modelling skills would have been an industry standard.

But all I can do really is speculate and go on evidence from the two examples that I have looked at in London.
 
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Adam W.

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So it looks like I've got a place on the MA, which will give me the opportunity to explore curved planed work and fan vaults.

Tops! \o/

The second frieze came out first try and it's now applied....


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The foliate mask chappies are looking suitably grumpy.

I'll attempt to shed light on the reasons why this frame was made in 1500 and what the symbolism represents in the frieze over the next few days, as it's heavily loaded with meaning and will also go some way in explaining why it's more than just a pretty container for an image.
 
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Adam W.

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So, I first came across a reproduction of this frame in the V&A museum and it contained one of my favourite Crivelli paintings of the Madonna and Child....... Remember the painting, it's important.

This was made by Zoe Allan, head of conservation at the museum.

Zoe Allan copy Tabernacle V&A.JPG


Then I came across it in a book.......Same frame, different ornamentation on the predella.
Tabernacle Frame.jpg

Then I came across part of what looked very much like it lying on a bench in the conservation department of the National Gallery in London......


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Then another bit of it, the capitals this time, in the National Gallery on a painting of Doge Leonardo Loredan......

That sight edge moulding looks very similar too.


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It was one of those things that kept appearing when I wasn't looking for it and not being one to walk past something which seemed to be calling out, I decided to find out more.

And of course the best way of finding out about this type of stuff it to try and make it in the original way. And whilst I was making the first one, I kept having loads of questions to ask about everything, so I went a visiting........
 

Adam W.

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So I dug deeper into how it was made by making one...obviously the best way to find things out about an object than the usual academic approach of just reading about it.

Initially, I thought the original was carved until I read the indepth analysis that the V&A undertook when they wrote their book on a selection of Italian renaissance frames.

Here they described the applied ornamentation as gesso. We use the word gesso to describe a mixture of rabbit skin glue and whiting (Calcium carbonate), which is applied to frames to support a gilded or polychromed finish.

I know how to make gesso, so I tried it out several times using all sorts of ratios of chalk to glue......It didn't work, as it shrank badly and looked like a dogs dinner.


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More research was needed into the renaissance way of doing things. Luckily there's a little book published it the 15th century by Cennino d'Andrea Cennini. We've all heard of him right ?

It's called "Il Libro dell'Arte" and he talks vaguely about two types of gesso, gesso grosso and gesso sottile. Italian was needed to figure this one out, but I already knew what grosso was, that's means thick or fat. Luckily I have an Italian native speaker to hand and she kindly explained that sottile means thin. A ha!

Lightbulb moment !

What does gesso mean then ? Well that means plaster. Not skim coat plaster, but what we call Plaster of Paris, (Calcium sulphate hemihydrate). Lets get proper about this, Ca(SO4).1/2H2O.

And I'm off down the experimental archaeology rabbit hole........
 
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Cooper

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What does gesso mean then ? Well that means plaster. Not skim coat plaster, but what we call Plaster of Paris, (Calcium sulphate hemihydrate). Lets get proper about this, Ca(SO4).1/2H2O.
Would this be the same as Victorians cast the repeat sections of the decorations in our cornice frieze? The reason I suggested that the original would have been carved was that I was told when plasterers made jelly moulds they had a very limited life and the patterns would have to be repeatedly used.

I agree that modeling in clay would be much easier. Years ago a friend wanted to have cast iron fire surrounds made in China and required a pattern based on an Edwardian apple themed design. He asked me to make the pattern. I tried all sorts of of ways, initially using sculpting wax as used for bronze casting, that didn't go well so I had a go with clay and achieved decent results but the only way I could get a tough pattern was use my clay model to make a silicon rubber mould which I could cast into. Not available to the Veniceiens!

This thread is so fascinating.
 

Adam W.

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That's called compo or composition and needs a wooden mould because it's filled under pressure using a whopping great wooden press. The trouble with compo is that it cracks when it dries and it takes a long time to dry, but it's a quick process to make repeat sections which can be cut, applied and gilded.

Zoe Allan made her casts from compo, but I'm doing a research project where there was no time limit to complete something and wanted to find out how the Venetians did it during the renaissance period.

Would this be the same as Victorians cast the repeat sections of the decorations in our cornice frieze? The reason I suggested that the original would have been carved was that I was told when plasterers made jelly moulds they had a very limited life and the patterns would have to be repeatedly used.
Forget what I wrote above. Yes your cornice is most likely plaster of Paris, but I'm not sure what the mould would have been made from. Compo is for picture frames.
 
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Adam W.

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So, I've been doing a bit of sketch modelling for the moulding around the sight edge. It's the quickest way to do this kind of thing and as I'm working in clay, I can add and take away elements as I go along.

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I just model a long strip and then pour a silicone mould which I take a cast of once and I can then take my time refining the initial plaster model without having to worry about it drying out.

Then I'll make another mould which I cast the finished mouldings from. I can re-use this mould for the other frame I've made and any other frames after that.

Back to CaSO4.1/2H2O and how to change it into CaSO4.2H2O tomorrow.

Oooo err !
 
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Adam W.

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It takes a long time for tomorrow to come in this house !

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The sight edge moulding is on and the grotesque ornamentation for the pilasters is underway and its time to get the CaSO4.2H2O out and make gesso sottile and pastiglia.

To convert CaSO4.1/2H2O into CaSO4.2H2O I had to resort to a bit of schoolboy chemistry and employ Dihydrogen monoxide H2O.

I combined 9 parts Dihydrogen monoxide to one part Calcium sulphate hemihydrate in a suitably sized laboratory approved container and continuously agitated the solution for 45 minutes until the exothermic reaction was completely exhausted.


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Actually, I dumped plaster of Paris into a lot of water in the gilding room bin and stirred it with a stick.

Once the initial part of the process was completed, the solution slaked for a further 30 days, with a water change each week and a stir twice daily.


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When 30 days was up it was drained in the gilding lab sink using bank robbers headgear and set it to dry for a further 30 days.

I then ground it up to a fine powder, sieved it and added it to hot rabbit skin glue mixed with 10 parts water to make pastiglia. This was used to fill the gap between the cast gesso and the joinery of the frame.


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There's a lot of gypsum in a small amount of glue and it's surprising how much the glue can take. Onced mixed I can keep it in the fridge for a week and use it to fill any cracks which appear in the joint, as it shrinks quite a lot when it dries. It needs to be warmed up in hot water before it becomes plastic enough to use and I apply it with modelling leaf spatula.

Here's the gap which needs filling. It's there because it was easy to snap the cast, so I had to make sure there was enough room for it to fall into place easily.


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You can buy CaSO4.2H2O (gypsum) in a bag as Gesso di Bologna and ovoid all this marlarkey, but I wanted the experience of doing it from scratch, as no one could tell me how it was done, apart from Cennini in his wonderful little book.

Next up gesso sottile.
 
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Adam W.

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Yet more swirling ornamentation, now the grotesque ornamentation has been modeled and applied to the pilasters.

I don't think there's any more room for anything else, it's certainly busy and compliments the carved chest quite well.

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A weekend of grinding gesso lies ahead to get ready for the gilding.
 

paulrbarnard

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Yet more swirling ornamentation, now the grotesque ornamentation has been modeled and applied to the pilasters.

I don't think there's any more room for anything else, it's certainly busy and compliments the carved chest quite well.

View attachment 114076

A weekend of grinding gesso lies ahead to get ready for the gilding.
I love how you have mounted a picture of a workshop in it.
 
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