Precise measurement of chemicals is a critical part of developing your film but it’s been difficult to get things exact. Until now! Hashim from Pushing Film shares an easy tip that will revolutionize the way you measure chemicals to develop film! Hit he jump for more!
Measure Chemicals The Right Way
If you’re going to develop your own film at home then you’re going to need to deal with mixing and measuring chemicals. It can seem daunting at first but Hashim from PushingFilm has a tip that makes the process super easy and accurate! Hit the jump for more!
The Problem With Volumetric Measuring
Most photographers will use some kind of graduated cylinder with volume markings to measure their chemicals. It seems simple enough to just pour in your chemicals and stop when the level of the liquid matches the amount on the side of the graduate.
But this is is not exactly precise in the real world.
Paterson graduates have thick embossed markings so it’s difficult to know when the desired amount is achieved. Do you stop pouring when the liquid is at the bottom of the marking? At the top?
And this gets even more difficult when you consider reading the meniscus.
Reading The Meniscus
Any solution inside a container is going to develop a meniscus which is the curved shape at the surface that happens due to surface tension. Convention says you should read the volume from the bottom of the meniscus but depending on your graduate and the volume you are measuring, this can be difficult to see.
Fortunately, there’s an easier way!
Measure Chemicals By Mass Instead Of Volume
Hashim points out that 1 gram of water is equal to 1 ml of water. As long as you have a reasonably accurate coffee or kitchen scale you can precisely measure water’s volume based on its mass. This 1:1 relationship works great for water but film developer (and other chemicals) typically weigh more than water.
To determine the actual mass we need the specific gravity of the chemical in question.
The Specific Gravity Of The Situation
In order to know the weight difference between a chemical solution and regular water you need to know the specific gravity of the solution. And as it turns out this is something that is listed in the datasheet of most developers.
For example, this document lists the specific gravity for all Kodak processing chemicals. And the specific gravity of D-76 (my black and white developer of choice) was 1.078 ±0.003 at 25°C. So all you need to do is multiply the amount of developer you need in milliiltres by this amount and you’ll get the weight of that developer.
I use D-76 diluted 1:1 so I need 300mls of stock solution for a 2 reel tank. This works out to 323.4 grams of developer and 300 grams of water.
Easy peasy!
The Temperature Matters – NOT!
I should mention that specific gravity of chemical solutions changes based on the temperature. For example, 1 gram of water equals 1 mililiter of water but only at 4°C.
When you raise the temperature to 20°C the mass of 1 mL of pure water is still right about 0.998 grams so you’re only out by around 2/1000 of a gram. And that’s close enough for something like film developing where exact measurement isn’t a life or death decision.
Of course, this applies to other chemical solutions like Film Developer as well.
The specific gravity of D-76 as 1.078 at 25°C. I used a Hydrometer Temperature Correction Calculator to determine the specific gravity at 20°C only drops to 1.077. Which is still pretty much the same thing.
So we’re good to go!
A Simple Formula To Measure Chemicals
Desired Volume X Specific Gravity = Mass For That Volume.
This simple formula plus a coffee or kitchen scale and measuring chemicals to develop film is a breeze. No more questions. No more guessing. Just measure and go.
I really only worry about any of this for the developer though. For stop bath and fix I just pour enough into my graduate to get it close to the right amount. I’m not mixing these chemicals so my only concern is using enough to cover the film in the tank.
Super easy!
The Last Word
I have a confession to make.
I studied photography in university. I literally have a B.A.A. in photographic arts. And I’ve processed thousands of rolls of film. This is something that I never considered until today. Literally 35 years after the fact!
To be fair, using mass to measure chemicals wasn’t something that was covered in our film technology classes. Maybe it’s because digital scales weren’t really a thing back in the 80s? Or maybe our profs just assumed we already knew this so they never brought it up?
Whatever the reason I’ve just been stumbling along using graduates this whole time. And there’s really nothing “wrong” with using graduates. Even though it’s not exactly accurate it’s close enough for most film developing needs. But it never hurts to to get things just right.
At the very least measuring using mass has made setting up to process film a few seconds quicker. So at least there’s that!
Specific-Gravity and pH Measurements of KODAK Processing Chemicals
What’s your take on measuring chemicals using mass instead of volume? Is this something you’d try or are you perfectly happy with your graduates? Post your ideas in the comments below and keep the conversation going!