Back in my youth, I was the kid who would stare at the glass of soda and watch the bubbles form on the side of the glass and rise in an endless stream to the surface. I was fascinated by it. How did the gas get into the soda in the first place? What caused the bubbles to form on the smooth glass? Why did they create this constant stream of bubbles? (We only had two television stations back then and no Internet, so it was easy to be fascinated by simple things.)
As an adult (soft of), I now understand the scientific principles behind my fascination. I'll explain it in a moment, but first, let's have a look at how you can create your own bubbly photos.
- Glass container - To avoid distortion select a container that has smooth sides. For this project I built my own (very tiny) aquarium out of some picture frame glass that I had lying around. I cut the glass with a standard glass cutter and assembled it with clear aquarium grade silicon.
- Clear soda or sparkling water - Choose something without added sugar to avoid a sticky residue when cleaning up
- Water - For the images in this post I mixed the soda in a 1:1 ratio with water. In many instances straight soda will create too many bubbles making it harder to control your shot
- Kitchen spatula - Bubbles will form on the glass surface - they're unavoidable. The spatula can be used to easily remove them in between shots
- Background material - I like the elegant look of black velvet so I draped a piece of it behind the container. Of course, different colours can help create a totally different look. For another photo project that involves black velvet check this out.
- Aluminum foil - Place a piece of aluminum foil under your container to help reflect some light back up at your subject and to catch the inevitable spills and drips that will occur. You can also use some foil to act as a bounce card
- Light source - I used a single compact fluorescent light to illuminate each of the subjects in this post. Placing the light at a shallow angle to your subject will create some interesting definition and avoid glare on the glass.
- Subject - Small colourful fruit works great but any object that will fit in your container may be worth experimenting with.
Just the fact that you are photographing your subject in a liquid that is separated from you by a piece of glass adds a whole new dimension to this project. There are two important challenges to be aware of.
- Most fruit is buoyant, and even if it is not, the coating of bubbles will likely make it so. This means that your subject will probably move around a bit unless you can stabilize it. For many of these shots I just held my subject by hand. However for some I skewered the fruit with a toothpick or piece of wire to help control its position. For the cherries shot above, I used a small clip to help hold them in place. You can also wedge a piece of foam into the container and use toothpicks to help hold your subject.
- The bubbles that you are trying so hard to capture can also be a pain in the... They will constantly coat the glass so have that spatula ready to wipe them away in between almost every shot.
For all of these photos I used my Olympus OMD E-M1 Mark II and the m.Zuiko 60mm f/2.8 macro lens attached to my Manfrotto tripod. Since the bubbles will move, you will need to be aware of your shutter speed. I have found that I can go as slow as 1/60s with good results. As well, I was using a macro lens at close distances, so I also needed to be aware of how much depth of field I was achieving. All macro lenses have notoriously shallow depths of field. An aperture of f/8 should be adequate for most subjects. With your shutter speed and aperture in mind, adjust your light source and/or ISO in order to maintain those settings.
To help guarantee better sharpness throughout the image I used the focus stacking feature built into the E-M1 Mark II. This provided me with 1 stacked image and 8 separate shots from the sequence that I could choose from if I needed to. Because of this I used a larger aperture setting than the f/8 recommended above.
The dark background will effect your camera's attempt to properly expose the shot. It will try to lighten the image making your subject look overexposed. As such, you may need to adjust the exposure compensation by stopping it down. For the images here I brought down the exposure value between -0.3EV to -1.7EV. The reverse would be true if you are using a lighter backdrop. You would likely have to bump up the exposure value.
The amount of post work required will largely be a matter of choice. I typically add a slight curves adjustment from within Lightroom and may bump up the vivid slider to enhance the colours of my subject. The tool that gets the most use however is the healing brush and/or the clone tool. The bubbles can form so quickly on the glass that it's quite likely there will be a few unwanted ones in your image. In the photo below I opted to leave the bubbles as part of the composition.
Since I was using the focus stacking feature on the E-M1 Mark II, I had 8 RAW images to select from along with the final stacked shot. For some of the images I selected 3 or 4 shots and used Photoshop to stack them. This allowed for more control over the final image.
Now, back to my childhood curiosity.
How does the gas get into the soda in the first place?
The gas in soda is CO2 (yes, the climate change gas). As it floats around in our atmosphere it naturally dissolves in water. There's lots of it floating around in the oceans right now. If water is cooled it can hold even more CO2. Add some pressure and it holds even more. That's what they do in bottling plants - cool the water and inject the CO2 under lots of pressure. When you open your bottle of soda, you are releasing that pressure and the gas comes out of solution. Shake it or warm it, and it comes out quickly because you've added some energy.
What causes the bubbles to form on the smooth glass?
Well, the glass isn't all that smooth. At least not at the microscopic level. Dust, dirt or tiny imperfections in the glass create a point where a change of state can occur - in this case from a liquid to a gas. These are called nucleation sites. This is the same process that causes frost on windows or raindrops to form. It's also why my beer foams so much if I didn't clean the glass well enough.
Why do they create this constant stream of bubbles?
When the buoyant force of the tiny bubble is stronger than the hold against the nucleation site the bubble is released and a new one starts to form at the site. This happens very quickly and so you end up with a stream of bubbles.