[Bill_Toge]

oleth-X has very different physical properties to ceteth- / steareth- / ceteareth-X - it’s a wedge-shaped molecule rather than a linear one, so it takes up much more space at the water/oil interface, and therefore they can’t be used interchangeably

with DMDM hydantoin, the major concern is temperature; these products have to be mixed and filled at high temperatures (60+ °C), and DMDMH will not survive an extended filling run that hot

[Bill_Toge]

it depends on titratable acidity more than the pH itself; from my experience, the lowest level of acidity at which I’ve observed consistent self-preservation is around 25-30 mg KOH/g

over several years we made dozens and dozens of batches of this product, and others with  higher acidites, and never had microbial growth in a single one

[Bill_Toge]

with O/W it’s good practise to include both a high and low HLB emulsifier, in order to maximise stability - if you can add an ionic emulsifier as well, that’s even better

[Bill_Toge]

if anything, under-preservation is more of a problem than over-preservation

put it this way: if you constantly feed someone a subtle poison, they’ll eventually get used to it, but if you blow their head off with a shotgun, they’ll never get the opportunity to do so

[Bill_Toge]

having worked with poloxamer 407, the genuine article is a white powder that lumps up in water, generates some foam on mixing, and takes a long time and a lot of shear to dissolve/hydrate in the absence of any other additives

in alcohol, it will not dissolve at all at temperatures below 20 °C

if your material doesn’t meet this description, it’s probably not poloxamer 407

[Bill_Toge]

DeedeeUkulele said:

Bill_Toge said:

like many amines, tranexamic acid oxidises and turns yellow/brown over time

Thank you, I wasn’t aware of that. I didn’t think it was the tranexamic acid because I didn’t find any data on it specifically turning brown. 

it’s a very common phenomenon with amine-containing organic compounds dissolved in water

for instance, at my last place we had an old sample of 90% monoethanolamine that had turned dark orange due to oxidation; when I ordered a fresh sample, it was completely colourless and had a much sharper odour

[Bill_Toge]

like many amines, tranexamic acid oxidises and turns yellow/brown over time

[Bill_Toge]

in my experience it’s very, very, very slow to dissolve and hydrate, and the process gets slower at high concentrations

[Bill_Toge]

0.1% is enough, more often than not

[Bill_Toge]

it is possible for cocamide DEA to form an N-nitrosamine, but only if your formula contains nitrite salts, organic nitrites or bronopol; without any of those ingredients, it won’t happen at all

[Bill_Toge]

sodium phytate is easier to find, does the same job, and dissolves more easily

[Bill_Toge]

homogenising the formula destroys PEG-90M and other long-chain resins of that type; your best bet is to disperse it in glycerine, or something else it’s not soluble in, then add it with stirring (no shearing!) until it’s fully hydrated

[Bill_Toge]

I agree with the previous respondents - that’s a photoshop job

using ingredients like that on the lips is a dangerous and very, very slow process with no guarantee of any results; plus, glycolic and ascorbic acids are insoluble in oil, meaning they’ll have little or no effect

[Bill_Toge]

Teluca, who manufacture hair colourants of all kinds, also have some excellent resources available, including a colour chart showing what can be achieved with particular combinations of bases and couplers

a tip from personal experience: if you want to mix colours, use one base with multiple couplers, or one coupler with multiple bases

if you try to combine multiple bases with multiple couplers, it becomes an absolute disaster zone

[Bill_Toge]

from my current job, the most challenging formula was a 15% azelaic acid serum - as azelaic acid is both hydrophobic and highly polar, it dissolves efficiently in very few solvents, and the ones it does dissolve in (dimethyl formamide) are highly toxic

the solution in the end was to formulate it as an emulsion with a highly polar oil phase (butyloctyl salicylate) - it worked, and it’s since become one of our best selling products

[Bill_Toge]

I also made numerous futile attempts to replicate Chinese-made styling pastes based on their ingredients lists, until I started ignoring the lists altogether and working from first principles

[Bill_Toge]

at my last place, one of our customers wanted to expand their range with an ointment, consisting of petrolatum, mineral oil, cetearyl alcohol and cetearyl ethoxylate; as the company had ample experience with hot-fill products, the formulation itself was not difficult, but processing it was

if you filled it too hot, it’d become rock-hard and brittle once set - you had to shear it to a smooth paste just below the melting point of the cetearyl ethoxylate and fill it below that temperature, and if the temperature got too high, the cetearyl ethoxylate would melt again and cause the end product to become granulated rather than smooth

but once we cracked the manufacturing method, we were then able to develop a paraffin-free formula, stabilised with castor wax, which allowed more flexibility on the filling temperature (at the time there was a great deal of controversy over paraffin-based ointments starting/aggravating fires)

[Bill_Toge]

iron and salicylic acid form a purple/red complex, but the colour change is usually instant

my best guess is that salicylic acid is slowly being released from willow bark extract, and it’s complexing with a source of iron

is your water deionised?

[Bill_Toge]

azelaic acid is not very soluble in anything - your best bet is to make the product an O/W emulsion with a very polar oil (e.g. a salicylate ester) as the oil phase

[Bill_Toge]

the silica is most likely fumed silica, which gels oils and makes them less fluid

[Bill_Toge]

make sure the electric systems are properly earthed, make sure there’s nothing inside the vessel that generates sparks, and keep the lid shut wherever possible (in order to prevent the release of flammable vapour)

there are more advanced measures that can be taken, but these cover the basics

[Bill_Toge]

are your samples very aerated at the point of filling?

if there’s enough of it, air being released from an aerated product could pressurise the container

[Bill_Toge]

your acrylates copolymer thickener is very likely to have been knackered by rhe salt, and your product has lost viscosity as a result

as for the pearl effect, if you’re not using a premixed pearliser, you need a lot more SLES, or a lot less glycol stearate, to see the effect

[Bill_Toge]

I’ve found a couple of useful substitutes for petroleum-based ingredients in colour cosmetics - Pelemol P3D from Phoenix Chemical (INCI: Dilinoleic Acid/Propanediol Copolymer) has the anti-lubricant properties of a high-viscosity silicone oil, while Viamerine 10,000 from Aldivia (INCI: Oleic/Linoleic/Linolenic Polyglycerides) has adhesive properties similar to a high molecular weight polyisobutene resin

[Bill_Toge]

hexylresorcinol is a good material for reducing dark circles under the eyes - you only need 0.5-1.0% for it to be functional