Tin chloride mordant

[Julian Cossmann Cooke]

Jo Kirby et al suggest that using tin chloride as a mordant for cochineal pigment yields something that is not translucent.  Is that always true of tin chloride or just in the case of cochineal.

 

Pictures are of cochineal pigment using aluminum potassium sulfate versus tin chloride.

[Davide Sora]

Tin chloride is interesting for the color more towards magenta with cochineal, what Kirby says about opacity worries me a little but I've never tried it, so I look forward to your opinions when you try it in the varnish
 

[Urban Luthier]

love to hear how one shifts cochineal to red -- I always get magenta when I use alum as a mordant 

[Davide Sora]

23 minutes ago, Urban Luthier said:

love to hear how one shifts cochineal to red -- I always get magenta when I use alum as a mordant 

I must confess that the only cochineal I used until now is from Kremer, fixed on alum and very bright red, for this reason I would like to try to make it to get magenta (maybe using alum and tin chloride together).

 

I make madder lake fixed on alum and is always red, more or less bright or dark depending on temperature of solution. (see Jo Kirby)

[Urban Luthier]

Yea me too -- madder always turns red with alum -- or brick red. I've use potassium carbonate to extract the colour for both madder and cochineal (and precipitate the lake). It is very base and I'm wondering if this has anyting to oo with the magenta of the cochineal lake. 

Sorry I'm not a chemist! 

[JacksonMaberry]

At least with rosinates, I've found better results with chlorine salts rather than a sulfur salts. I wonder if aluminum or zinc chloride might be worth a stab? Love the experiments, Julian. Thanks for sharing your results. 

[Julian Cossmann Cooke]

3 hours ago, Urban Luthier said:

love to hear how one shifts cochineal to red -- I always get magenta when I use alum as a mordant 

I don't know that it is the difference maker, but Kirby's tin chloride AND alum recipes involve heating before and after the potassium carbonate is added to the water and organic material.  They also prescribe distilled water in both cases.  The amounts of chemicals also are pretty similar as I recall.

Which leads to the question: all other factors being equal, what is it about tin chloride that yields magenta rather than purple or red?

[Michael_Molnar]

1 hour ago, Julian Cossmann Cooke said:

Which leads to the question: all other factors being equal, what is it about tin chloride that yields magenta rather than purple or red?

 

The tin atom attaches to the cochineal molecule (anthraquinone - carminic acid). The charge on the tin atom (ion) twists or distorts the molecular structure, which in turn changes the light absorption property. Magenta means that the molecular structure now absorbs more blue, green (cyan) and yellow. Aluminum in alum distorts the molecule to absorb more blue and green and less yellow, producing red for which carmine is best known. You need to look at a color wheel to understand how colors are produced by absorption. 

The details, nevertheless, remain a puzzle, but I am sure there is somewhere a graduate student working on this for her dissertation.