=Please put in vegetable scraps=
The quality label clearly states that the first step in caring for aluminum products is to boil them in water to create an oxide film on the surface, as this improves the corrosion resistance of the pot surface.
This page explains with images how the color of the oxide film changes depending on the degree of boiling.
The quality label explains that a colorless oxide coating of the aluminum base color is applied, but even if a dark (light brown to dark brown) oxide coating is applied, it is an oxide coating similar to anodized aluminum called "boehmite" and is called aluminum hydroxide, so please rest assured that it is harmless to the human body.
<<The reason why the oxide film has turned black>>
By boiling the water, the neutral components of the water become alkaline, causing the oxide film on the aluminum surface to peel off and a new film called aluminum hydroxide to form. This film undergoes complex chemical reactions with the minerals in the water, causing it to appear black (or dark brown). (Tap water mainly contains the minerals potassium, sodium, potassium, and magnesium.)
The quality label also clearly states that the first step in cleaning the product is to boil vegetable scraps in tap water, which will leave the aluminum hydroxide coating colorless (retaining the aluminum base color).
We recommend and would like you to use "Boehmite," an oxide coating that has a clean aluminum base color and is not blackened.
It is believed that the components contained in the vegetables suppress complex chemical reactions with the minerals in tap water, forming a colorless oxide film on the surface of the pot.
Until now, it was thought that a similar effect could be achieved by adding oil.
Following a user's comment, we conducted another boiling experiment using tap water only, tap water with oil added, and tap water with vegetable scraps added.
Please refer to the images below (oxide coating A, B, C). In addition, for vegetable waste, you can also refer to the images of the boiling process.
The water is brown due to the scum from the vegetables, but once you discard the water, the surface of the pot will remain colorless.
The same results were obtained after repeated testing. (Since the product is boiled, an oxide film is definitely formed.)
However, results varied when using oil, and in some cases a darker coating was formed than when using tap water alone.
The particularly darkened part is shown as oxide coating B in the image.
Due to these different results from previous experiments, we have concluded that boiling with vegetable scraps suppresses the chemical reaction of minerals (in the water) on the surface of the pot and ensures the formation of a transparent oxide film, and we have now revised the quality label to clearly state that it is boiled with vegetable scraps only.
Oxide film A
<Tap water only>
⇒ Light brown
Oxide film B
<Mix oil with tap water and boil>
⇒ Brown
Oxide film C
<<The state immediately after throwing away vegetable scraps>>
⇒ Aluminum skin color/colorless
The process of boiling vegetable waste
Add vegetable scraps and boil for about 10 minutes. The water will turn brown due to the scum.
When the water is poured out, the pot returns to its original colorless state. The pot is left as it is, with the water level line still visible, and the surface of the pot is not wiped clean.
How to remove black spots
The quality label also clearly states how to remove the initial oxide layer if it turns black.
① Add water up to the blackened part of the pot
②Add sliced lemon
③ Boil for about 15 minutes
Removes dark spots and returns to original color
Similar results can be obtained by adding citric acid, which has a higher acidity.
Also, the surface of an aluminum pot will inevitably darken over time.
This solution is also an effective way to clean your pot. You can restore a beautiful, clean surface to your pot over and over again!