Invisible ink using an orange juice
Every science experiments must start with an aim. That means while doing an experiment you must think for what purpose you are doing this experiment. That should be in your mind so that you can go through the entire experiment very easily. In this experiment your aim must be to show how the acidic properties of an orange juice can be used for making an invisible ink. See Fig 1.
Principle of an experiment
Remember that there will be a principle associated with each & every experiments in chemistry. So I think you have got an idea regarding the nature of the experiment that is going to be described here. The acidic nature of the orange juice plays an important role in the chemical reaction that takes place here. This is a simple experiment. The next point you have to keep in mind regarding this experiment is related to the requirements, procedure & conclusion of this invisible ink experiment.
For conducting this experiment, you will require the following items. See Fig 2.
4.Small paintbrush that have fine bristles
5.Heat source including sunshine or light bulb
Procedure to make invisible ink using orange juice
For doing this experiment, it is better to use a fresh orange fruit. Cut it into two pieces so that you can easily take the fresh juice from this fruit by squeezing it. It is better to use a half portion fruit for this purpose. Collect the orange juice in a small bowl. Before adding the orange juice to the bowl, make sure that it is well cleaned.
In the second step you must keep the brush into the bowl containing the orange juice. Make sure that the bristles are covered with sufficient quantity of orange juice.
Take the white paper & you must write or draw anything on it using the brush (already immersed in orange juice). See Fig 3. If needed, you can recoat your brush several times. Allow the paper to dry for several minutes.
After drying the paper, you may not be able to see what you have written or drawn in it. Then hold your paper to a heat source & after sometime you may be able to see some changes on the paper. That means you may be able to see a brown color along the picture or message (what you have written on the paper). See Fig 4(After dried using an heating source).
Chemistry of the reaction
The highly acidic orange juice (acting as an ink here), when applied to the white paper, weakens it. So what happens is when this paper is placed on a heating source, the acid content present in the paper (even after the fruit juice is dried) will turn brown revealing the whole message or drawings made by you.
Care needed to be taken while doing the experiment
Parents/teachers should watch their children who are doing this experiment. The presence of heating source in this experiment is a dangerous one. So care should be taken while doing this experiment.