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Old 06-03-12, 12:35 AM
dbclemons dbclemons is offline
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Default Adding eggshells to gesso mix?

Does anyone here add ground up eggshells into their gesso mixture? I had a conversation with a fellow artist recently who works in tempera and said she grinds her eggshells into a powder and combines it with marble dust as her solids component of the hide glue gesso mix. She claims it makes a brighter surface. I thought it curious that I'd never heard of that practice before, but sounded like a good use of what many tempera painters would likely just discard. I've read that eggshells are mostly calcite and some protein, so I can't think of any risks.
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Old 06-03-12, 02:29 AM
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Salamander Salamander is offline
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show us pics of your experiments! Ought to work
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Old 11-03-12, 03:29 PM
dbclemons dbclemons is offline
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My preliminary tests are encouraging. One thing that bothers me, however, is this protein part and how it may change with age.

Some people grind the egg shels into a powder and consume it for the calcium content or use as part of a fertilizer. The recomendations I've read to prepare them is to first dry the shell in heat to make them more brittle, either slowly in the sun or oven.

I washed a few empty shells and removed as much of the slippery insides as possible, and when I first broke them up I noticed there was still a thin membrane that couldn't be easily removed. I cooked the shells from three eggs in a 200 degree oven on parchment paper for about 30 minutes and noticed that the bright shells had turned slight darker. I'm fairly certain it's the protein membrane that was being roasted, but I need to try and find a better way to remove it, otherwise I'm afraid if it's added to the gesso powder it will only darken more over time.

This darkening might not be a major problem, I feel, since I can't see myself ever using very much of this in a mix. Three large eggs made only about 1 tablespoon of powder.

I can't think of any strong advantage shells would have over gypsum or marble dust, and even possibly having a slight disadvantage with this protein content. Still, using a little at a time may be better than just throwing them away as waste. It needs a little more investigation.
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Old 11-03-12, 03:39 PM
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Koo Schadler Koo Schadler is offline
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Thanks for all the info db. I love these sorts of experiments. I've never heard of using shells myself - and as you say, chalk or gypsum are inexpensive and work well so there isn't a great need. But its fun to understand these things better. Keep us posted please. As for the waste issues, egg shells are great in compost - they break down well and feed the soil, so there is a good use for them.

Koo
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Old 12-03-12, 02:28 PM
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I use cage free eggs, and they tend to be brown, so for me that would be a problem.

Cage free is major issue with me; I know it's not the same as free range, but it is far better than industrial cage farming.

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Old 13-03-12, 01:34 PM
dbclemons dbclemons is offline
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I thought of that too, Bron. They do have a brighter white inside so they grind up to a brighter shade. If you use only a small amount mixed in with your other solids the coloring wouldn't be very noticeable. Some cage free breeds lay white eggs also. They can even be blue and slightly pink. I don't know if it would be possible to bleach that out, but it would likely be more trouble than it's worth.

My little coffee grinder also didn't get as fine a powder as I'd prefer. I've read that boiling the shells first before drying them is a good way to kill any bacteria that might be present.
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Old 13-03-12, 02:36 PM
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Koo Schadler Koo Schadler is offline
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I was thinking about the subject of getting a brighter ground, and it might be worth mentioning that not all chalks and gypsums are equal in that regard – some are whiter than others. For instance, some of the French chalks have a rosy tint; I was given a chalk from Texas that is a definite off-white, nearly grey; etc. So if one is looking for an especially bright, pure white ground its important to start with a truly white chalk or gypsum. A connoisseur could buy from all the different suppliers, line up the options, and see which appears the brightest…

Another trick that many of you already know is to add a bit of titanium white pigment to your gesso. Not too much (substitute no more than perhaps 10% of the chalk) because it does not have the same crystalline properties of chalk/gypsum and too much T.W. would make too soft of a ground. But a bit will increase the opacity and hence brightness of the ground.

I mention the above because, while I love the experimentation with egg shells, these other options are tried and true – no potential downsides as far as I know.

Koo
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