Hello chemistry nerds!

I got into dyeing, first using commercial products, then experimenting with DIY vegetable-based dyes, because if there’s a more expensive and labour intense alternative to buying a ten dollar product, I’m all over it. Naturally, I started extracting lake pigments to make paints out of my used dye baths.

Before you say it, yes! I do want lower quality paints that fade faster and take two days to make.

I use alum (aluminium phosphate) and soda ash (sodium carbonate) to precipitate the pigment, followed by drying and grinding.

Since this journey began I noticed some dyes just won’t work for pigments. I tried hot, cold, waiting, stirring, light jazz, more acid, more base, but the bitches won’t precipitate. Cranberries were my most recent failed pigment (but they dyed real nice.) There was lots of colour left, and I even tried a new dye batch with fresh cranberries, but it had the same result.

SO! I’m wondering:

  1. What makes a dye substance a better candidate for a lake pigment? Are there chemicals the alum can latch onto easier than others?

  2. If alum doesn’t work, could a different metallic salt work better?

  3. Why does every blog say not to use your dye equipment for food? What if I clean it super well?

  4. Are there other chemicals I can try? For funzies?

  5. Are there any other cheap, convenient products I can replace with five hours of destroying my kitchen?

  • Wrufieotnak@feddit.orgEnglish
    4·
    3 days ago

    Hi, I am not working with dyes, so I can’t provide answers to those specific aspects, but give you some general chemistry one.

    1. Precipitation means that the dye is not interacting as well anymore with the solvent (water in your case) after adding the prec. agent. This is possible via 2 mechanisms. Either the agent interacts with the dye directly or it changes the properties of the solvent (most often via the pH value) and thereby weakens the interaction. From what I gathered on wikipedia, lake pigments most often work through the first mechanism. The prec. agents you add are salts, made up of positive charged cations and negatively charged anions. Normally, water is a great solvent for ions, meaning they are soluble. The dyes however are organic compounds with one part that is very ionic, meaning very water soluble, and one part which is not ionic at all, which in general means not water soluble.
      When you add the prec. agents, they first dissolve in water as well, but then its dissolved cations are interacting with the negatively charged groups on the dyes. That means the dyes are orientating themselves around the cations, which means that the non ionic parts are looking outside. Imagine it like a hedgehog rolling together -> only spikes on the outside and the spikes don’t interact with water -> they precipitate.
      With that background: some dyes are better interacting with water than the prec. agent, which means they don’t precipitate as well. For other dyes, the “outside” is still interacting well with water, which means again: no precipitation, because even the combined form can be dissolved.
      From what I gathered, the alum phosphate is not the precipitation agent itself, but rather to dilute the dye. But yes, your thinking is correct in that some groups better attach to the metal cation than others. Or since we are talking about organic compounds: The fundamental groups are the same (Hydroxy & Carboxy acid groups), but its rather the geometry of those groups that makes them latch onto the metal cation better.

    2. Definitely! But it completely depends on the mechanism of the precipitation as explained in question 1. I saw calcium and strontium mentioned, so probably magnesium works as well.

    3. Because you add something to the dye which you can’t remove with cleaning: the precipitation agents! And you definitely don’t want to eat aluminum salts! So no, as chemist: please don’t eat anything where you added any salt besides table salt, if you don’t know specific that it is allowed to be eaten (tofu is precipitated by sepcific salts and ok for consumption for example). also, it might be that the concentrated form of the dye is not healthy for consumption

    4. Since I am not working with dyes, I can’t answer you, but I was wondering what you mean here: Do you mean chemicals for precipitation or chemicals for dying?

    5. Make your own fermented vegetables (sauerkraut, kimchi, raddish, …)! You can season it exactly as you like and its delicious!

    So sorry, a lot of “can’t answer that”, but I wanted to provide at least a bit of basic chemistry background. So let me give you an additional part of info you didn’t ask for:

    From what I found, one of the pigments in cranberries is cyanidin (wikipedia link) and that explains why you can’t precipitate it: it doesn’t have any carboxylic acid groups, which are normally the groups that most strongly interact with metal cations. But in the german wikipedia of the article it mentions, that the chloride version is nearly insoluble in water. So you could try adding simple table salt and see if that precipitates it. Second idea: it is also soluble in ethanol, so you could try and extract the berries with as high percentage alcohol as you have.

    • Wren@lemmy.todayOPEnglish
      2·
      2 days ago

      Amazing! This is more than I expected, thanks for taking the time.

      1. Super helpful. I have just enough chemistry know-how to understand. The resources I found were either over my head or not detailed enough, this is perfect.

      2. I’m gonna try ALL the salts.

      3. Good. Good to know. (oops)

      4. Like if grass is the best dye but Big Green Dye doesn’t want us to know. Or if there was a way to make red cabbage explode.

      5. Perfect. I already have a lot of leftover cabbage. I simmer it in salty vinegar water for a dye bath anyway. (Before I add the poison.)

      bonus: I’m gonna try both of these today.

      Thank you!

      Edit: Follow up question, if it’s not too much. Do you know if there’s something that makes certain dyes adhere to plant based fibres better than animal-based and vice-versa? My cabbage dyes suck for wool (even trying different mordants, including alum which, from my observation, sticks to wool and the dye stuff,) but adhere to cotton and rayon very well.

      • Wrufieotnak@feddit.orgEnglish
        2·
        2 days ago

        Glad I could be of some help.

        I’m interested to hear about your experiments.

        Regarding your edit: sadly no, that is outside of my expertise.