[Bill_Toge]

the best way to stop oxidative dyes from darkening is to keep their contact with air to an absolute minimum; this is why these products are always sold in tubes or sachets (i.e. airtight containers)

whenever we manufactured the bulk liquids for oxidative dyes we always covered the surface with a plastic film to stop them darkening

as for the product which thickens when mixed, it sounds like the developer (pH 2-3) contains a peroxide-stable carbomer or similar polymer which is neutralised and thickens when the dye (pH ~10) is mixed with it

[Bill_Toge]

@Belassi just got to warn you that MEA has a nasty habit of turning formulas yellow/brown, particularly at high levels; it’s something to bear in mind if the colour is an important aspect of this product

[Bill_Toge]

@Belassi that sounds more like glyceryl stearate to me; in my experience, glycol stearate and glycol distearate are both effective pearlisers in shampoo/surfactant bases

[Bill_Toge]

@Belassi, I have used it before, and I wouldn’t use it again unless there was no alternative whatsoever

the reasons being that it’s difficult to disperse (it’s only soluble in hot surfactants, and it dissolves very slowly), and that the viscosity it imparts is extremely sensitive to temperature variations; a product which is acceptable at 20°C becomes water-thin at 35°C and thickens to jelly at 10°C

as a direct substitute I’d suggest using Antil 120 Plus or Antil 127 from Evonik/Degussa, if you can source them

[Bill_Toge]

because there is no scientifically rigorous, legally defined or universally recognised definition of “natural” (as demonstrated in the discussions above), we avoid making “natural” claims like the cliche

if you want to claim green credentials it’s better to follow a recognised and documented standard, e.g. Ecocert, than it is to indulge in puffery, wordplay and vague hand-waving

as my old boss used to say: never make a claim on the pack that you can’t defend in court

[Bill_Toge]

further to @Sarah‘s comment, the full text of that opinion can be found here:

http://ec.europa.eu/health/scientific_committees/consumer_safety/docs/sccs_o_136.pdf

(skip to page 103 for the conclusion)

[Bill_Toge]

soap/surfactant combinations in liquid products is an unusual technology unique to Unilever

the key material is the sodium cocoyl isethionate, as it apparently forms liquid crystals with fatty acids, giving the product a cream-like structure while retaining the foaming properties of a conventional shampoo or bodywash

Unilever have filed numerous patents related this technology - US7807612 (B2) is an illustrative recent example, and makes for interesting reading; also, it’s not just an exercise in theory, as various liquid products in the Dove range are formulated this way

it was something we attempted to replicate in a previous job, but the project was abandoned for practical and IP reasons

[Bill_Toge]

in Europe the formula has been standardised since last year, as per directive 162/2013 - denatured alcohol now contains 3% v/v isopropyl alcohol, 3% v/v methyl ethyl ketone and 1 ppm Bitrex as denaturants

the biggest practical problem with only using Bitrex as a denaturant is that it’s easy to remove by distillation; adding isopropyl alcohol and methyl ethyl ketone makes distillation much more difficult, if not impossible

[Bill_Toge]

@kbasali the only way you can totally achieve the effect you want is by physical removal of the hair, e.g. with waxes and/or an epilator; chemical depilatories will help remove the hair, but they won’t do the whole job on their own

[Bill_Toge]

I work for a company which occasionally makes shampoo for dogs

we use a combination of SLES, TEA lauryl sulphate (an efficient cleaner, but more mild than ALS or SLS) and cocamidopropyl betaine at about pH 8, and nothing else apart from the preservative

also you’re totally right not to experiment on your kittens; ethical issues aside, it’s best for your own safety

[Bill_Toge]

what’s your surfactant system, and what other ingredients have you got in there?

also, how long have you had samples at 25°C?

(I ask because that viscosity loss may simply be much slower at 25°C than it is at 40°C, and as time goes by you may observe it at 25°C too)

also, not directly relevant to this thread, but that egg yolk could potentially be a huge microbiological risk, depending on how much you’ve got in there and whether or not it’s sterilised

[Bill_Toge]

@Rahma and let’s not forget those ‘brilliant’ British academic scientists who start off with an agenda and manufacture the evidence to ‘prove’ it

(e.g. Darbre, who published the paper fuelling the “parabens cause breast cancer” scare; the paper which is full of fundamental scientific errors and statistical cherry-picking that would have got any industrial scientist sacked)

[Bill_Toge]

as I see it, there are two big practical problems here:

1. thioglycolate is the only chemical depilatory which is a) effective in the way you want, and b) legal to use; unfortunately, it smells of sulphur and rotten eggs

you can mask the worst of the smell with the right perfume, but you can’t eliminate it altogether

2. since Turkey’s cosmetics legislation is in line with that of the EU, skin peels would be considered borderline medicines, as they have a physiological effect as well as a cosmetic effect

I would strongly suggest you seek legal advice about what you can and can’t claim on such a product, and whether or not you can actually sell them for home use; all the documents I’ve seen so far have indicated they’re meant for professional use only

[Bill_Toge]

try using a low molecular weight poly(ethylene oxide) resin, e.g. Polyox from Dow

be advised these are sensitive to shearing, so it’s best to add them at the end

Polyox brochure

[Bill_Toge]

magnesium ascorbyl phosphate is a good one, as it’s reliable, relatively safe and more stable than ordinary vitamin C

kojic acid and alpha-arbutin are also effective, but they’re very expensive and some safety assessors take issue with them as they’re hydroquinone-alikes/hydroquinone precursors; if you decide to go down this route, check beforehand that your safety assessor is OK with them

[Bill_Toge]

while I agree with other respondents that CTAC won’t do anything to help with stability, experience tells me the separation is almost certainly down to the oils kicking out the pearliser; cutting them back to <0.1% should improve matters

[Bill_Toge]

@Chemist79 only snag there is that you’ve got to read up on the relevant patents very thoroughly if you go down that route; it’s still an intellectual property minefield even today

[Bill_Toge]

ethyl cellulose is miscible with most solvents bar water; I’d suggest mixing all the other ingredients together and adding water at the end

also, cellulose derivatives tend to swell very slowly at room temperature  - if you want to cut down your processing time, heat the mixture up to 30-40°C and mix it thoroughly

[Bill_Toge]

@Chemist79 mineral oil which has a viscosity of 21 cSt or less at 40°C has been classified as an inhalation hazard, due to several reported cases of suffocation; at higher viscosities it’s harmless

[Bill_Toge]

I suspect it’s down to product aesthetics/skin feel more than anything else; HEC gels have short flow and are well suited to skincare, while HPMC gels have long flow and are better suited to surfactant systems

[Bill_Toge]

what are you planning to disperse it in?

I agree that 325 mesh would be too fine; mixing and filling a bleaching powder that fine, on an industrial scale, would be a serious respiratory hazard and a major fire/explosion risk

from a safety perspective, coarser is definitely better!

[Bill_Toge]

floral/herbal perfumes, e.g. lavender, are good for masking this type of smell; they’ll not eliminate it altogether, but they should take the edge off it

[Bill_Toge]

in my experience, preservative-grade caprylyl glycol and ethylhexylglycerin are virtually odourless, so I doubt it’s either of them

I’d guess it’s either isodecyl neopentanoate (an ester which is relatively volatile compared to the other ingredients, and thus, further to @milliachemist’s point, the most likely thing to smell like fruit), or something they’ve not declared on the label

[Bill_Toge]

can’t speak for US suppliers, but European industrial grades of nitrocellulose (e.g. Walsroder from Dow Wolff) are not classified as explosives as their degree of nitration is low and they’re supplied pre-wetted with solvent in sealed containers, so they’re easier to transport

however, even with these precautions in place it is still EXTREMELY flammable, and will ignite at the slightest provocation - warmth, static discharges, mechanical shock - making it the most dangeous material likely to be encountered in cosmetics manufacturing

the fact that once it’s on fire, the fire is self-sustaining and very difficult to put out does not help either!

(I used to work in a paints and coatings factory years ago, and remember that the wood varnishes, containg nitrocellulose, were made and filled in a separate, easily cordoned-off building since it was such a huge fire risk)

[Bill_Toge]

styrene copolymers have been used to opacify cosmetic products for years with no safety issues; the most important aspect from a toxicological point of view is that they’re usually huge molecules (on the order of 500,000 Da), so little if any is absorbed into the body

as for thickeners, I’d suggest using a cellulosic thickener such as hydroxyethylcellulose, carboxymethylcellulose or Methocel, since they have long flow properties, allowing the product to be easily dispensed from a bottle onto a brush, but they also gel the product enough for it not to drip everywhere