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Posted By: Scott Rowley
Total Posts: 15
Joined Date: Dec 31, 2014

Ceracolors medium didn't melt until above 140. So a slow bake wouldn't work. A quick heating and quick cooling would work best, I think.

Also, I'm not sure the layers need to be heat fused. If I take a little medium and rub it in to the first layer and when I paint over that it seems like the layers should dry fused.

Posted : Oct 2, 2017
Posted By: Scott Rowley
Total Posts: 15
Joined Date: Dec 31, 2014

I do love the pigment. 

The wax was definitely starting to glisten and soften before 140 degress F. It might be enough to keep the temperature in the 130s long enough for the heat to penetrate through the layers of paint.

Posted : Sep 29, 2017
Posted By: George O'Hanlon
Total Posts: 2253
Joined Date: Jun 15, 2004

We have observed this color shift or loss of chromacity due to temperature above 140 degrees F when grinding the pigment. We have to use water-cooled grinding equipment and carefully monitor the temperature.

George O'Hanlon Technical Director Natural Pigments
Posted : Sep 29, 2017
Posted By: Scott Rowley
Total Posts: 15
Joined Date: Dec 31, 2014

I did some tests on the vivianite, and it seems like I can fuse a ceracolors painting with minimal color change.


My equipment is far from scientific. I just have a toaster oven and a cooking thermometer. So that's what I used. To adjust the heat I turned the heat dial and opened the oven slightly if it climbed too quickly. I maintained a reasonable heating consistency, but needless to say, not precise. I don't know how much lag there was in my thermometer, so the temperatures could have gone a couple of degrees higher than the reading on the thermometer.


For each test I painted a line of Vivianite in water only, and a line of Vivianite in Ceracolors Gel Medium. I cut the papers in half and saved one side at room temperature. The other side got a small pile of beeswax granules. The granules were about 1 mm in diameter. 


I put the first test paper in the oven at 133 F and gradually increased to 136 F over three minutes. There was no color change in the wash with water. The Vivianite in gel medium was just a little more saturated from the curing of the paint. The granules of Beeswax had softened and fused enough that they no longer rolled off the paper, but the granules were still somewhat distinct. That might be enough to fuse a Ceracolors painting, especially a thin one, but I'm not sure.

 

I put the second test paper in the oven at 135 F, and maintained the temp between 135 F  and 142 F for 5 minutes. There was a barely discernable color shift toward green. But barely discernable. For me, it was an acceptable color shift. The beeswax grains had completely fused and about 1/2 of the volume had soaked into the paper. 


The third I maintained between 140 F and 146 F for 6 minutes. The color change was more discernable. But still very slight. The painted stripes were still quite blue in color. The granules of Beeswax were completely soaked into the paper.

In my opinion all three samples maintained the intense Vivianite blue. So I should be able to fuse a painting with minimal color change. Less color change than is inherent to most art mediums.  Just saturating the pigment with Ceracolors Gel caused more of a shift toward green than the heat, even on the third test.

I also heated a sample to 170 F over 8 minutes. And there was no fading but there was a strong shift from blue to Grey.The intense Vivianite blue was lost. 


It occurs to me now that I should have used shavings of dried Ceracolors medium, because if they fused that would be a stronger proof that a Ceracolors painting would fuse at those temperatures.  I'll do that when I have a chance.

Posted : Sep 29, 2017
Posted By: Scott Rowley
Total Posts: 15
Joined Date: Dec 31, 2014

George,


I didn't think I was telling you anything you didn't knowSmile.  For me this is a positive finding, because this is a preventable problem. When I read that vivianite had faded in paintings by Vermeer, Rembrandt and other artists from the time period, I worried that it might be something inherent to the oil medium. Now there is another possible explaination. I am going to keep using vivianite.  If I provide warning to the customer, maybe on the back of the painting, then I can do something to prevent the fading.

I will do some tests. The fading in oil paintings seemed to have something to do with how efficiently the dried film conducted the heat to the pigment.

Posted : Sep 27, 2017
Posted By: George O'Hanlon
Total Posts: 2253
Joined Date: Jun 15, 2004

We have not tested vivinite with Ceracolors, but we are aware of the issues with vivianite incluing thermal sensitivity. If you exposed vivianite to brief durations of this temperature it may not damage the pigment. Please test this for your application.

George O'Hanlon Technical Director Natural Pigments
Posted : Sep 27, 2017
Posted By: Scott Rowley
Total Posts: 15
Joined Date: Dec 31, 2014

I find vivianite very beautiful, so I've been trying to find answers to why vivianite sometimes fades and other times doesn't. I've found a couple of studies where vivianite fades on heating. Temperatures as low as 140 F can start a color change. Major color change happens around 170 F, These temperatures could be reached when a painting is re-lined for preservation. So that gives us something to watch for, and something to instruct buyers about. My source is a PhD dissertation: Mineralogical Analysis of Historical Paintings, from 2015, Cermakova Zdenka. 

I wonder if I can fuse ceracolors at temperatures less than 140 F. Or if mixing some fiber paste in each layer might help adhesion.

Posted : Sep 26, 2017

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