1. What Is the Black Mark on the Toe of Indoor Shoes Made Of?
A household management advisor explains that the black marks on indoor shoes are a mix of dirt, water, and oil [5]. They say things like sand, dust, art paint, calligraphy ink, food spills, sweat, and skin oils pile up together. However, this explanation covers the whole shoe, not just the rubber toe part. It is said that detergent does not easily remove stains from the rubber part, so eraser-style cleaners or melamine sponges are suggested [6]. When using these, ask an adult for help and check the care instructions on the shoe.
For tires, it is explained that carbon black particles are mixed into the rubber to increase wear resistance [7]. But this information is about tires, not school shoes. As for why black marks appear only on the toes, we are left with the idea that dirt piles up there, but no more than that.
2. Why Do Japanese Schools with Western-Style Education Still Make Students Change Shoes?
Why do we change shoes at school in the first place? Japanese homes have a habit of taking off shoes before entering. However, when the school system was introduced in 1872, school buildings changed to Western-style structures [3]. Even so, the habit of taking off shoes to enter indoors remained.
Before World War II, many students reportedly changed into tabi socks (traditional split-toe socks). The spread of changeable shoes like today's indoor shoes happened a bit later.
3. How a Tabi Company Made the First "Front-Rubber Shoes" for Schools
In Kurume, Fukuoka Prefecture, there is a company started in 1873. It began as a tabi-making company [2]. Around 1927, they started making "front-rubber shoes" for children, which are the predecessors of indoor shoes. These shoes had triangular rubber pieces inserted into the top part.
It is not accurate to say this company invented indoor shoes. The sources suggest it is better to see them as one of the companies that made a shoe that became a predecessor to indoor shoes. The connection between a tabi company and rubber shoes is an interesting clue when thinking about the shape of indoor shoes.
4. How Ballet Shoes Influenced Indoor Shoe Design in the 1950s
Today's indoor shoes look similar to ballet shoes. There is a theory that the name "ballet shoe" comes from being made with reference to ballet pointe shoes [3]. The term "uwaguri" (indoor shoe) appears in sales materials for retailers in 1957 [1]. In the following year, 1958, ballet-shoe-style indoor shoes are said to have been released. This is introduced by an encyclopedia site citing industry group explanations, not an announcement from a manufacturer itself [1]. There are also explanations that they spread gradually in schools. These years are rough estimates mentioned in explanatory articles.
5. What Are the Elastic Band and the Colored Toe on Indoor Shoes For?
Ballet-shoe-style indoor shoes use an elastic tape about 2 cm (about 0.8 inches) wide threaded through the top to adjust the size, allowing you to slide your foot in [1]. Some products use colored rubber on the toe, which is used for things like class identification.
In an introduction by Moonstar, it is said that the elastic band and simple designs like red or blue on the toe and outer edge have hardly changed since they were first sold [2]. On the other hand, improvements have been made over time, such as changing materials to prevent the sole from wearing down. Sometimes it is explained that "the rubber is to keep them from falling off." Here, we will stick to describing the shape.
6. What Are the Grooves on the Sole of Indoor Shoes For?
What are the zigzag patterns on the bottom for? The educational shoe page of Nisshin Rubber introduces types that use "Ame rubber" in the sole to improve slip resistance, and types that use shock-absorbing rubber in the heel [4]. However, that page does not have any description about the shape or role of the grooves. Here, we just include the manufacturer's introduction regarding rubber soles.
7. How Can You Test the Black Toe Mark Yourself with a Tissue?
You can try this today: Wipe the black part of your indoor shoe toe gently with a dry tissue. If color comes off on the tissue, there is a possibility that something from the surface has transferred. Even if no color comes off, you cannot decide for sure if it is dirt or the rubber's color. Compare where the black area is: at the tip, the side, or the heel of the toe. Wash your hands after wiping.
You can also try this when going out: Look at and compare indoor shoes with different toe colors or ways the rubber is attached at shoe stores or school supply sections. For official information, checking educational shoe pages of shoe makers or the Japan Educational Shoes Council might help you find explanations about materials and construction.