[Bill_Toge]

a quick and easy qualitative test for mercury would be to disperse some of your cream in hot water and add diphenylcarbazone

if the water turns dark blue/violet, there’s mercury in the cream

[Bill_Toge]

you’ll need to consult an analytical lab, this type of work is not done by cosmetic chemists

just out of interest, why would they have to be in the US?

[Bill_Toge]

the hydroquinone is polymerising due to the high pH and the high alkalinity of your product; the only way to stop that is either reformulate your product as a syndet bar (so it has a lower pH), or change the laws of thermodynamics

[Bill_Toge]

you’d be better off with a paddle stirrer

as your product gets more viscous, a magnetic stirrer will become totally inefficient

[Bill_Toge]

which colours are you using?

[Bill_Toge]

in my case it’s not so much the physical cost of the materials that puts me off making dozens of batches, as the limited time and manpower we have available in the lab; I work for a small company with a large throughput, and our entire R&D team consists of two people, myself included

if you sit down at first and think about the problem logically before you start making batches, and go after the most likely materials first, it (usually!) cuts out a lot of time that could be put to better use, particularly if the product itself takes a long time to manufacture

plus, it helps bridge your practical and theoretical knowledge, which in my book is never a bad thing

[Bill_Toge]

if you’ve got a mixture of oils with different saponification values, the best thing to do is to calculate a mean saponification value for the whole mixture

you can do this by calculating (sap value x %weight) for each oil, adding them all up, and dividing the whole lot by the total percentage of the oils

here’s a worked example, with totally made up figures:

30% w/w oil A, sap value = 117 mg/g
21% w/w oil B, sap value = 20 mg/g
28% w/w oil C, sap value = 235 mg/g

mean sap value = ((117 mg/g x 30%) + (20 mg/g x 21%) + (235 mg/g x 28%)) ÷ (30% + 21% + 28%)
= (35.1 mg/g + 4.2 mg/g + 65.8 mg/g) ÷ 79%
= 105.1 mg/g ÷ 79%
= 133 mg/g

[Bill_Toge]

if you do make sure you get some uranium-235 as well, so it stays heavy

[Bill_Toge]

if the batch is truly irreplaceable, it could be sterilised by irradiaton

how the price of irradiation weighs up against the cost of disposing of the batch altogether and starting again, I don’t know

[Bill_Toge]

@homeobiz I meant contamination from the production line, or from the packaging itself, not necessarily microbial

what material is your bottle made from, where was it manufactured, and is it manufactured under sterile conditions?

also: what’s the pH of your product?

(sodium benzoate at 0.1% is only effective if your product is very acidic)

[Bill_Toge]

if it’s inconsistent, that suggests contamination of some kind, or a packaging-related issue

what kind of packaging have you filled it into?

[Bill_Toge]

do they have financial backing and a business plan?

if so, the company I work for may be able to help - PM me for details

[Bill_Toge]

this is the text of the regulation itself; it applies to ALL cosmetics, regardless of who uses them, and there are no abrogations for professional users

the fact that these products are on the market doesn’t mean they’re legal!

[Bill_Toge]

@BartJ, the usage limits on salicylic acid are not a grey area at all; the limit @David stated is proscribed in Annex III/98 of the regulations

if you use a substance listed in Annex III outside the specified limits or for uses other than the ones specified, your product is not legally compliant as a cosmetic, regardless of whether or not it’s meant for professionals

[Bill_Toge]

also: does it separate if you put it through several freeze/thaw cycles?

[Bill_Toge]

does it also separate at lower temperatures?

and if so, how long does it take to separate?

[Bill_Toge]

I’d suggest you use a shear mixer to disperse the zinc oxide and silica, if you don’t already; if you still have the problem, omit one or the other and see if the problem still occurs

clays are chemically inert silicate minerals, can’t see them causing a problem

[Bill_Toge]

@David is correct: if you want an accurate result, the best method is titrating it with potassium permanganate

[Bill_Toge]

titanium dioxide will make your base more opaque

as for increasing the drying time, the best thing I can suggest is to use a solvent that’s less volatile than ethyl/butyl acetate, and reformulate your base from first principles

[Bill_Toge]

it’s also a very vague and open-ended question; I’ve read it several times now and I’m struggling to understand what exactly it is you want to know

[Bill_Toge]

@David you won’t need specialist equipment in the lab; the most appropriate precautions would be to use a dust mask at all times, don’t mix it using equipment made from any other metal than good quality stainless steel, and keep it away from moisture and sources of ignition

[Bill_Toge]

in my view you’d be best off seeking specialist advice

depending on the batch sizes involved and the particle size of the finished product, mixing and filling powder bleach can potentially be a HUGE fire hazard

because of this (and because our site in the middle of a residential area), we’ve always subcontracted it to a third-party manufacturer

[Bill_Toge]

@Kewell in my experience the LV models are good up to about 1,000,000 cPs, which you’re only likely to reach if you’re working with toothpaste or hot-fill styling products

@thebrain an RVDV-I with a heliapath is probably the best one for your purposes

[Bill_Toge]

before I make a comment, I’ve got a couple of questions:

firstly, where are you planning to sell this product?

secondly, does this yellowing also occur at lower temperatures?

[Bill_Toge]

if you want something of a similar solubility and in a similar price range, try sodium thiosulphate, or ammonium thiocyanate