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  • March 19, 2020 at 11:11 am #485501
    Namkha
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        Has anyone tried this? If so to what effect?
        What kind of chalk did you use?

        Thanks!

        March 20, 2020 at 10:04 am #962455
        contumacious
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            Are you wanting the maximum transparency? When I add chalk / marble dust / calcium carbonate it doesn’t really make the paint all that transparent, mostly just thicker.

            You might look at a transparent filler rather than a more opaque filler like chalk. Finely powdered glass or glass beads perhaps? Fumed silica makes a very transparent medium that works well for glazing if it is thinner and impasto with thicker mixes. Be sure to follow safety guidelines with fine powders.

            March 20, 2020 at 5:44 pm #962460
            Namkha
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                That’s great. Thank you.
                I have just read that somehow chalk makes the paint not only thicker but also more transparent. I’m going for thickness, but some transparency also would be great.

                Can you just grind up a piece of chalk or is there special chalk?

                March 20, 2020 at 11:01 pm #962456
                contumacious
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                    That’s great. Thank you.
                    I have just read that somehow chalk makes the paint not only thicker but also more transparent. I’m going for thickness, but some transparency also would be great.

                    Can you just grind up a piece of chalk or is there special chalk?

                    It would depend on what kind of chalk you have and how finely you can grind it. Most chalk today is not made of real “chalk” which is something called diatomaceous earth. Many contain clay instead. You can buy Whiting at most paint stores, marble dust and chalk from art supply sources and calcium carbonate from gardening supplies. It needs to be a very fine grit, like powdered sugar.

                    Adding powdered calcium carbonate (chalk, marble dust, whiting etc) will make the paint more transparent because you will be spreading out the pigment by replacing some of the volume with the chalk, but it will also tint it slightly more white, just not nearly as much as white pigment does. It will thicken it so you will need to add more oil or medium to regain the original consistency if you don’t want it to be thicker. Adding calcium carbonate will also produce a more matte sheen which can be helpful if you are glazing, to give the next layer a less slippery surface to bond with.

                    If maximum transparency is what you are after a transparent filler like I already mentioned, combined with transparent pigments will give you a significantly more transparent final mixture.

                    March 21, 2020 at 11:48 am #962457
                    contumacious
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                        I did a test today with some finely powdered calcium carbonate and PR177-Anthraquinone Red. I added more oil until the mix had the same consistency as the original paint. To my eye there was no increase in transparency, if anything the pure paint was slightly more transparent. Gloss decreased. It was slightly lighter in value and lower in chroma. It was nearly dry to the touch in an hour, while the plain paint was still fairly wet. I don’t have any powdered glass or diamond dust to test. I did not test fumed silica medium as I already know that it will be more transparent than the plain paint and thus even more transparent than the calcium carbonate added mixture.

                        There might be better or easier to use / obtain materials than powdered glass or fumed silica to add for increased transparency without increasing the oil to filler/pigment ratio which adding just oil or medium will do, or creating an underbound paint layer like you can get with solvent. Perhaps someone can chime in with additional suggestions.

                        ———-

                        March 22, 2020 at 4:41 am #962454
                        Gigalot
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                            You can make your opaque paint more transparent with adding chalk but already transparent paint can’t increase it’s transparency. Chalk filler is more translucent than transparent. The best chalk for painting is paint grade, finest synthetic sediment of calcium carbonate made in industry from lime stone.

                            March 22, 2020 at 7:45 am #962458
                            contumacious
                            Default

                                You can make your opaque paint more transparent with adding chalk but already transparent paint can’t increase it’s transparency. Chalk filler is more translucent than transparent. The best chalk for painting is paint grade, finest synthetic sediment of calcium carbonate made in industry from lime stone.

                                Some good information. Thanks. I will do a test with some opaque pigmented paint and see what happens. All I have used the calcium carbonate for in the past was for making putty mediums and for adding some tooth to and increasing absorbency of my grounds. Gigalot – have you ever used powdered glass or glass beads mixed with paint?

                                March 22, 2020 at 10:00 am #962461
                                Namkha
                                Default

                                    You can make your opaque paint more transparent with adding chalk but already transparent paint can’t increase it’s transparency. Chalk filler is more translucent than transparent. The best chalk for painting is paint grade, finest synthetic sediment of calcium carbonate made in industry from lime stone.

                                    If it’s from lime stone why do you say “synthetic”?

                                    Thank you.

                                    March 22, 2020 at 10:02 am #962462
                                    Namkha
                                    Default

                                        It would depend on what kind of chalk you have and how finely you can grind it. Most chalk today is not made of real “chalk” which is something called diatomaceous earth. Many contain clay instead. You can buy Whiting at most paint stores, marble dust and chalk from art supply sources and calcium carbonate from gardening supplies. It needs to be a very fine grit, like powdered sugar.

                                        Adding powdered calcium carbonate (chalk, marble dust, whiting etc) will make the paint more transparent because you will be spreading out the pigment by replacing some of the volume with the chalk, but it will also tint it slightly more white, just not nearly as much as white pigment does. It will thicken it so you will need to add more oil or medium to regain the original consistency if you don’t want it to be thicker. Adding calcium carbonate will also produce a more matte sheen which can be helpful if you are glazing, to give the next layer a less slippery surface to bond with.

                                        If maximum transparency is what you are after a transparent filler like I already mentioned, combined with transparent pigments will give you a significantly more transparent final mixture.

                                        Thank you for all of this. Very helpful.

                                        March 22, 2020 at 8:19 pm #962459
                                        contumacious
                                        Default

                                            You are welcome.

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