How to make Poinsettia pigment into ink? Like many families, this winter we had bought a red poinsettia plant to decorate our kitchen, and now that it's losing its leaves, I had the genius idea to extract the red pigment. The activity proved a success, and let my 5 yr baby girl amazed (and us too). The pigment was extracted by letting leaves soak in 96% alcohol overnight in a closed container in a hot spot, then filtering the solids and heating the solution until alcohol evaporated for the most part, also adding a few drops of lemon juice to increase acidity and transform the brownish liquid into a blood red tint the that now has the aspect of an ink. Unfortunately, we were unable to use this ink to basically anything, as most mediums like regular paper or white paint are neutral or high pH and turn the poinsettia ink from red to any other color, like blue or green. 

As you might have gathered by now, I am not a chemist, and I have no knowledge in the matter beyond high school classes from the old days. I did understand thou after reading this article that changes composition and color with pH. 

So what I ask for, if at all possible, is a method described in plain terms and using household accessible chemicals to stabilize this red ink in order to use it, for instance, to paint on paper without losing its intense red color. (at least for a few hours or days)
I think that would be hard, you could try to use a mordant to convert a dye to a pigment, you can use Alumina $\ce{FeSO4}$  or $\ce{CuSO4}$. There is an article that explains it in detail how to use Poinsettia for colouring silk fabric.


  Rawat, Bhawana, et al. "Color fastness properties of silk fabric dyed
  with poinsettia leaves." MAN MADE TEXTILES IN INDIA 48.11 (2005): 418.


You can try to soak a thick paper in a solution of 1-5% of $\ce{FeSO4}$  with your dye heating gently. 

Another solution could involve a different medium, like arabic gum mixed with citric acid.