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Thread: Sketching at the telescope - a one stop shop for astro sketching

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    Default Re: Sketching at the telescope - a one stop shop for astro sketching



    Very well said Alex.
    Even winslow Homer used photographs in his painting process.
    I am interested to know if it is possible to use a fixative on the dry brush method similar to the fixative used in chalk pastel, not only for preservation but for building up. Any thoughts on that?
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    Mark

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    Default Re: Sketching at the telescope - a one stop shop for astro sketching

    Quote Originally Posted by Eagleheaf View Post
    I am interested to know if it is possible to use a fixative on the dry brush method similar to the fixative used in chalk pastel, not only for preservation but for building up. Any thoughts on that?
    WARNING: Materials science lesson below!

    DO NOT USE FIXATIVE OF ANY KIND WITH SOFT PASTEL ASTRO SKETCHES!

    You will destroy your work.

    Fixatives are all some type of varnish. As it happens, the refractive index of varnish and that of calcium carbonate (the chalk constituent of soft pastels) happens to be essentially the same. What this means is the pulverised chalk that is in the soft pastel, it is opaque due to the smashed up edges of the crystals. When you wet this powder, the varnish effectively fills in and removes the crushed surface of the crystals, and due to having the same refactive properties, the chalk is rendered transparent, leaving just the coloured pigments.

    If you have ever used a fixative on any chalk based astro sketch (which is very soft/faint by its nature), you would have noticed that the sketch "disappears" and is ruined. Man, I've lost a few sketches because of this. So today I don't use fixatives on my soft pastel sketches.

    There is one way to overcome this problem. It means using not chalk based media such as soft pastels, but powdered zinc oxide or titanium dioxide. These compounds do not share the same refractive index property of varnishes, so when you spray these compounds with varnish, they remain as when you applied them and do not disappear.

    Another thing about powdered zinc oxide and titanium dioxide is because they are more opaque than soft pastels, they can be used with soft pastel sketches to give more "punch" to white highlights. There is only so much punch or opacity that soft pastels have, and these two compounds are much more opaque.

    HOWEVER! Word of caution about powdered zinc oxide and titanium dioxide! As a sketching media their greater opacity means they are much less forgiving than soft pastels. Lay these on too heavily and you will not be able to tone them down. They are very aggressively opaque, if there is such an expression.

    Below is a test piece sketch I did to try out the titanium dioxide powder pigment I bought. The majority of the M8 sketch is done using white soft pastel. The bright core of M8 was done using the titanium dioxide powder. This stuff is REALLY a hard task master! I do not use the titanium dioxide powder on its own to sketch with - it is much too difficult and unforgiving to use. I only use it for nebulous highlights. The majority of my sketching is still done using soft pastels, so again I don't use a fixative on my work. The best way I have to protect my work is putting each piece into a plastic sleeve presentation folder.

    Attachment 174323 , Attachment 174324 , Attachment 174325

    There are no health concerns regarding zinc oxide or titanium dioxide how they are readily available. These powders when sourced from art supply stores are used as pigments for those people who want to make their own paints. These compounds are also used in the food industry and pharmaceuticals as food and medicine dyes - your white pills often contain these compounds to bulk them out and add a white brilliance to their appearance. Zinc oxide is one of the active ingredients in sun screen lotions too. As paint, food and pharmaceutical dyes these compounds are not ground fine enough to be "nano" size. It is possible to acquire these compounds in nano sized particles, but these should be totally avoided!

    With regards to building up layers, I have had no problem developing layers with the Mellish Technique. I certainly do not expect to produce a complex structure in the one brush stroke - it won't work that way. Instead I build up the layers starting with the softest/faintest, and working up the brilliance as I develop the different details and shapes. This applies for both white and black, and I often use them together in the different layers.
    Last edited by mental4astro; 03-08-2018 at 01:18 AM.
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    Default Re: Sketching at the telescope - a one stop shop for astro sketching

    Thank you Alex! I appreciate your expertise and very much.
    Mark

    92 Messier, 4 Planets, other cool stuff.
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    Default Re: Sketching at the telescope - a one stop shop for astro sketching

    Love this form of art, can't wait to give it a try!! Thank you for all the great information.

 

 
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