Color shift in formulas containing salicylic acid

Formulating

Color shift in formulas containing salicylic acid

Posted by joseg on August 16, 2014 at 12:04 pm

I just recently made a clay mask with 1% salicylic acid dissolved in 15% propylene glycol. My base is the typical xanthan gum, bentonite and kaolin formula. After a week, I started noticing some red-pink streaks coming out and color has been shifting further since then. When I made the batch, my initial pH was around 2.9 and decided to adjust it with NaOH up to 4.0

After thinking about this issue, it just hit me that I have made in the past a shower gel with 2% salicylic acid dissolved in a base of SLES, Cocamide MEA and CAPB. At that time I was asked to adjust also pH up to 5.0 or so. When put up on stability, all samples started turning red as well.

Is this something common when working with salicylic acid? could it be because of the pH adjustments? Thanks in advance.

fareloz replied 1 month ago 8 Members · 9 Replies
9 Replies

DavidW

Member
August 16, 2014 at 7:42 pm

I have been working with Salicylic acid in a clay mask as well. We have made about 30 or so different versions and in each one after a few days we get some purplish liquid that comes out. I know in some clear serums we have made in the past using this sometimes it takes on a pinkish tint too. I would have to check my notes in my office to see if it had anything to do with pH
nasrins

Member
August 17, 2014 at 12:45 am

I have the same problem with salysilic acid
Chemist77

Member
August 17, 2014 at 4:25 am

@joseg There is a ferric chloride test for aspirin to detect the presence of salicylic acid, pure aspirin would return negative while presence of purple coloration would confirm the presence of salicylic acid. For your clay mask formula I am guessing you have some iron impurities which are giving this violet coloration with salicylic acid.
I pulled up this info from some interesting articles and I am sure with the iron impurities present it would be intrinsic to have a color drift. But I always suggest discretion and further reading and research.

cheers
MakingSkincare

Member
August 17, 2014 at 1:45 pm

Yes, with salicylic acid, you’ll get a lot of discoloration if there’s divalent cations like Iron.
Bobzchemist

Member
August 17, 2014 at 10:24 pm

I’d bet that with enough chelating agent, this would stop being a problem…
joseg

Member
August 17, 2014 at 10:55 pm

@milliachemist thanks for your great help!

@bobzchemis I was thinking the same at first but from what I’m seeing, bentonite has Fe impurities so I’m not sure if I would need to end up removing bentonite from my formula

I will make 2 more batches, one with chelating agent and one replacing bentonite and will let you guys know the outcome

Thanks a lot!
Bobzchemist

Member
August 18, 2014 at 5:15 pm

Bentonite is composed of clay platelets - nothing short of HF can remove them from your formula. The few small molecules of chelating agent will form a complex with the iron contaminates in the bentonite - nothing gets removed through that mechanism either. I don’t know if I can communicate the size differential properly - think of a pencil eraser compared to Mt. Everest, maybe that will help.
Dtdang

Member
March 22, 2024 at 9:00 pm

do you find out what causes color changing in your formula?

Thanks,

Danh Dang
- fareloz
  
  Member
  March 25, 2024 at 8:34 am
  
  It is stated in the comments - iron ions from bentonite, salicylic acid reacts with iron and creates this purple color.
  
  If you get same result without bentonite that most likely you have water not deionized enough