Originally Posted by Two23
you can give the cop a dose of phenidone, to make him happy
I am by trained a certified calibration expert. A 6 dollar mass set from Amazon or other place will not be very calibrated. Tripple beam can go down to like .1 grams and lower depending the model you get.
Last edited by Steven Ruttenberg; 11-Jan-2019 at 08:37.
In the 70s I sold Ohaus scales, among other photo items, to a small camera store along the Delaware river in PA. This store, in a small town, not near a city, was buying several scales each month. After a few months, on one stop there, I asked the owner where he sold all of these scales? He explained that there was a group of “farmers” that were growing a type of hemp and were constantly being busted by the cops and their equipment was confiscated and they had to replace it all, among the necessities of their business was the Ohaus scales!
Steven, Instant Mytol has to be mixed before usage, you may want 300ml stock for a 600ml 1:1 of it to make 12 4x5 sheets, then you may need to measure 0.045grs of phenidone (0.15*300/1000) for that. If your scale makes 0.1grs...
This $11 one is class M2, norm , OIML R 111-1 : https://www.amazon.com/American-Weig...bration+set+m2
A M2 calibration is aproved to sell gold...
Nothing official about it, but remember that 1cc or ml of water is 1 gram. If you want to verify how your jewelry/pocket scales work, you can put 10ml of water in a small medicine measure which you'd zero'd the scale with dry, and it should be 10g. Or zero it with an empty 2-3ml plastic pipette and draw up some water to the line, and measure it's mass again for smaller amounts.
Yes, you are right, by weighting water volumes we can see if scales are good enough, this solves most of the problem.
Anyway checking a jewelry scale is more difficult. Imagine next case: a jewelry scale performs acceptably at say 10grs, but it has some dirt inside provocating an slight vertical friction, and it has a hysteresis of 30mg, the phenidone for 300ml (12 4x5 sheets) of the instant mytol is 45mg...
This $11 kit allows to check if the scale also works well with low (say 45mg) loads, as it even includes a 10mg weight.
Well, $11 to be sure that one nails the chemical formulas... the kit will last for ever...
In darkroom practice the water method would be suitable for the food scale, the jewelry scale IMHO needs more the calbration weights, the one I have came with the weights, if you browse amazon you will find than many come with weights, but many don't include small weights...
When I prepare an emulsion I always check the scale first, for the moment I'm making small batches to test, and there are several reagents that are used in small quantities and requiring precision, iodine for example, and of course the sensitizing dyes. It's for this that I use the jewelry scale, because I'm not mixing developers at the moment.
Even water has a standard and depending on where it is from, it can be off. For example if you use a water softener, the density will be less than one.
They have triple beam and other mechanical a scales that go to.01 and smaller. The issue with any scale that could measure down to.045 gms would need to be shielded all around or the mass will be off due to just breathing and minor air currents. Even temperature fluctions. Then add in the error of scale, say +/- 10% and now you could have anywhere between.0495gms -.0405gms while scale in theory reads exactly 0.045gms. If you're saying you need precisely 0.045gms or formula won't work, your toast.
My point is this is not an exact science so how precise/accurate do you really need to be so long as proportions are maintained. Also, one can, with experience, read down to half of what scale resolution is, but not on a digital scale.
Anyway, whatever works best for someone is the best scale to use.
And having been a Deputy, scales, little baggies, white residue, brow residue and yellow residue pretty much got you a ride to hotel from hell. Or if you fought a little, you got stomped on and then a free ride.
I never said otherwise. Still, for stuff like phenidone of which you need fractions of a gram, stock solutions are more convenient and arguably more consistent than weighing the dry powder for every batch of developer you make. Since I generally mix several small batches of various developers a week, I suppose I would know.
This approach also works very well for mixing small volumes of pyrocat stock, which would be of interest to Steven in particular.
Steven, if mytol formula says 0.045gms for 300ml, perhaps it will work nearly the same with 0.040 or 0.060gr, being a +50% quantity the second case, the but anyway you require an scale with at least 0.01gr for that, and if possible a 0.001gr one. I presented the phenidone case to point that even in that extreme situation you can avoid making dilutions.
As koraks mentioned, dilution solves the phenidone issue, if this was the single problem...
but anyway if a pocket sized scale solves all dosification for ingredients in the grams range...
My view is that a food scale is first what we need, but if we often manage quantities under (say) 15gr then the cheap jewelry scale is a must.
Me at lest, I'm really happy to use one, I found it extremly useful and convenient for the DIY emulsions, in that case consistency has many factors, and the last you want is having any uncertainty in the small quantities you mix, when I started with DIY emulsions it was a nightmare, bottles of dilutions everywere, and always calculating the watter addition, all to not have accurate doses because sometines not having enough reagent quantity to make a dilution volume. $10 investment and all problems evaporated.
Last edited by Pere Casals; 11-Jan-2019 at 07:14.
As long as you are consistent and use same scale for all your weighing, then the errors will all be the same and you will get consistency. I was just pointing out, that to be accurate and precise if that is your goal, that a tripple beam will do that and that for the really small stuff it will need to be shielded. If you want digital, here ya go, but ain't cheap.
https://www.hogentogler.com/veritas/...CABEgInAvD_BwE
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