Indicator droplet art

The inspiration for making pictures from droplets of chemicals first came  from a Chemistry Club session at our school. I had just made a batch of red cabbage indicator, so we decided to test it out on the CLEAPSS microscale indicators sheets.1 On these printed practical sheets (either laminated or placed inside a plastic pocket), droplets of chemicals are placed on top and pushed together and the resulting reactions can be observed on a microscale. When you are finished, you simply wipe them clean. Bob Worley’s website2 has some examples called “chemistry on a plastic sheet”. The colours of the indicators looked amazing — they were so bright against the white background, and I got thinking — how could we develop this further? 

A little later, I needed a Christmas activity for our Chemistry Club, and I wondered if we could create a picture using droplets of acid and alkalis — a bit like "painting by numbers" but with different pH droplets. Hence, the “ChemisTree” was developed. My prototype used droplets of buffer solutions with red cabbage indicator, and to add a bit for extra “fanciness”, there was real "silver tinsel" — by the displacement of silver by copper! We ran it in the club, and it was a hit. We used little plastic dropping bottles for convenience — but it seemed to work.

 pH 1 = red; pH 4 = purple; pH 9 = indigo; pH 11 = dark green pH 14 = yellow.Figure 1. First image created using red cabbage indicator.

Once I saw how visually appealing the ChemisTree was, I decided to venture into creating other images from the droplets. The lizard template was drawn. I quickly realised the size of the droplets for more intricate designs would need to be smaller. I needed to do a little experimentation to get the droplet size right. Droplets from a 1 mL plastic pipette are around 33 μL. Once the indicator has been added, the droplets are very large and have a greater likelihood of merging into the adjacent droplet. Fine-tipped 1 mL plastic pipettes will deliver about 20 μL, so droplet control is improved. For my pictures, I use a 5-50 μL micropipette. I think I usually make droplets of less than 10 μL. I only have one micropipette tip — which I carefully clean out between solutions! 

The templates are either placed in a plastic pocket or laminated, then the droplets of chemicals are applied directly onto the plastic. Personally, I think plastic pockets work better because the process of lamination can give slight undulations on the surface of the plastic, which could then result in your droplets merging together. I thoroughly enjoy the challenge of creating a picture in colourless solutions, then "revealing it" with the use of the indicator. 

When I first posted the lizard image on Twitter, I was really surprised by the response — there is no scientific value to this and it’s just a bit of fun — but quite quickly I received "likes" from around the world! 

A hand-drawn template of a lizard.Figure 2. Template of lizard placed in a plastic pocket. The resulting art uses droplets of red cabbage indicator. Download the printable PDF version of this drawing (PDF).

A lizard design using colourful drops of indicators.

Figure 3. Lizard art: the resulting art uses droplets of red cabbage indicator.

These pictures have all been made in my home. I like to use readily available household chemicals such as vinegars, citric acid and bicarbonate of soda solutions. Most of the pictures are made from red cabbage indicator, but I use methyl orange for vibrant reds and oranges, and sometimes beetroot for very dark colours. I do have a few “laboratory” chemicals, such as 0.1 M hydrochloric acid and a little bit of sodium hydroxide solution for the beautiful "yellow" with red cabbage. I have started to develop the technique to include basic chemical reactions, and used this on my kingfisher picture (Figure 4). 

A kingfisher mostly made from mini droplets showing different colours of blue, yellow and red.Figure 4. Kingfisher: The blues are complexes of copper(II) sulfate with ammonia and sodium hydroxide.

I am really excited about other chemical reactions that could be included in my pictures, and I have recently tried out potato starch and iodine solution to create a panda.

An image of a panda made up of mini droplets in blue-black drops using iodine (Lugol's solution).Figure 5. Iodine panda: Droplet chemistry in motion using iodine (Lugol’s solution) with potato starch. The iodine is diffusing faster than I can pipette, resulting in the lovely blue-black drops.

A Mendeleev droplet image created to celebrate the International Year of the Periodic Table.Figure 6. Mendeleev: To celebrate the International Year of the Periodic Table, this image was created by varying the pH of tap water with a red cabbage indicator.

Photographing the images is very tricky, and involves me taking the completed image out into the natural light to try and reduce "glare" off the plastic. The photographs really do not do the droplets justice as each one sits so perfectly and bright on the plastic. Seeing is believing, and the droplets look like tiny jewels in the sunlight. Beautiful! 

It can be frustrating at times when the droplets do not behave, but it is actually really relaxing and fun making these pictures! 

I continue to tweet out my chemical droplet artwork as the CrocodileChemist @CrocodileChemi1

Top tips for making droplet pictures

  • Make a good strong batch of red cabbage indicator — you can dilute down later if need be.
  • Make a colour chart at the side of your image to determine the colours your solutions are going to give. Red cabbage is a natural indicator and different batches may produce different colours. Use a range of pH solutions — or try blending them to achieve the colour you are looking for.
  • Use a pipette that will deliver the smallest droplet possible. 
  • Apply constant pressure to the bulb of the pipette — the solution needs to remain at the pipette tip so there are no air bubbles and “spluttering” doesn’t occur.
  • Any droplets that merge can be removed using a Q-tip and re-done. 
  • Wipe clean when you’ve finished and the template can be re-used.


  1. Consortium of Local Education Authorities for the Provision of Science Services (CLEAPSS) is a UK resource that provides schools with safety advice and model risk assessments in science and design/technology at both the secondary and primary levels. In doing so, it also provides ideas for exciting and engaging practical activities that fire pupils' imaginations and then, unlike many other sources of ideas, goes on to show teachers and technicians in detail how to translate the ideas into safe and exciting experiments in the classroom. CLEAPSS advice and documentation is recognised by the UK Health and Safety Executive and the UK Department for Education. Much of the material is behind a subscription wall, but the CLEAPSS YouTube channel is open source.
  2. Bob has more posted puddle ideas and videos. for small video clips of chemical reactions.

Bob also noted that Isobel had wanted to call her artwork “pH art”, but Bob pointed out it might be considered inappropriate — if you sound it out and know Bob’s humour, you will understand why.