What is the most rare coin of yen, (by age)

We use many coins, and we think tha value of money is same (in same kind). But is it really true? If  you look at this blog, your vision about coins will change.

Quick Look at the contents

1.What kinds of coin in Japan?

2.Survey method


4.Cause consideration


1.What kind of Japanese coins?

Do you know Japanese coins? Japan have six kind of coins, 1yen, 5yen, 10yen, 50yen, 100yen, and 500yen. If you even know about Japanese coins, please skip this section.


Composition:  aluminum 100%

Design:  ①young tree


Composition: copper 60%-70%,


 zinc 40%-30%

Diameter: 22mm

Design:  ①ear of rice, ②gear, ③water, ④two-leaf


Composition: copper 95%

, zinc 4%-3%, tin 1%-2%

Diameter : 23.5mm

Design: ①“byodoin howodo” temple, ②an evergreen


Composition: copper 75%, nickel 25%

Diameter: 21mm

Design: ①chrysanthemum


Composition: copper 75%, nickel 25%

Diameter: 22.6mm

Design: ①cherry blossom


Composition: copper 72%, zinc 20%, nickel 8%

Diameter: 26.5mm

Design: ①paulownia,② bamboo,③ “tachibana”

And all coins is written “when is it made” in red circle (ex.50yen)

 *“syouwa”1~64=A.D.1962~1989. “heisei”1~31=1989~2019. “reiwa”1=2019

2.Survey method

Every time I used coins, I record that “when this coin made” in a month, especially I recorded 

5yen about 10 months.

I didn’t exchange in bank, so this date is near to coins we use everyday.

The answer of “when this coin made” is written in red circle (look image)

And I cant record much money about 50yen, 100yen, and 500yen. So this brog’s topic is only 1yen , 5yen, and 10yen.(


This is the graph of result each 5 years.

1yen (total 62)

5yen (total 158)

10yen (total 72)

This graph is totally graph of these three, and this is represented by percentage of each coins.

*Bellow this, I called this result “my date”.

These graphs represent the follows

  • All coins were made during from 1962 to 2021
  • The number of coin’s issues is declining trend
  • 5yen’s changes is nearly 10yen’s one.
  • 1yen truly cant see

The follows are probable cause

  • These changes dependent that the number of issues….Ⅰ
  • The materials are different, so aging is changed…..Ⅱ


  • ⅠThese changes dependent that the number of issues

All Japanese coins are made by “Nihon Ginko”, so I searched this and made graph.

This graph is divided each 5 years.

*Bellow this, I called this result “bank date”.

The red square means that my date don’t have coin made 1952~1961.

4.Cause consideration

Next, now I compare each kind of coins, and I made line graph (left) and scatter plot (right).

“ ” means If the two date (my and bank date) have correlation, the

will be big, and

can changed from 0 to 1


there are high correlation, and almost, my date depends on bank date.


This date show that there are normal correlation, and my date mutually related with bank date.


There are few correlation.

yen 1 5 10
R^2 0.8838 0.6677 0.1806

This result show that about “1yen” probable cause Ⅰ is true, but about “5yen” that is false.

Why did this result?

I think, the answer is probable cause Ⅱ.

If 10yen are rustier than other coin, the old 10 coin should be thrown away, so the deference (between my date to bank date) occurred.

I searched “how rusty” about each materials.

Review material of each coins

1yen : Al 100%, 5yen : Cu 60%-70%, Zn 40%-30%, 10yen : Cu 95%, Zn 4%-3%, Ti 1%-2%

metal Electrode potential(V)
this Cu(copper) +0.4
Zn(zinc) -0.8
Al(aluminum) -2.4
Ti(tin) -1.8

This chart show “how rusty”. If the value of electrode potential is high, the material is stable(=hard to rust), ex. The value of gold is +1.5.

if the probable cause Ⅱis true, the large of that will be “Cu>Zn>Al”. (the stability of coins will be 1>5>10yen)

but the result is…

 the large of that value is “Cu>Zn>Ti>Al”.

This is the strange result. I searched more, and I discover that cause.

That is oxide film.

But this is difficult to explanation, and this blog will be long, so I will finish this topic.


This investigation teach us that the rare coins (by age) are exist, and this is partly related with the number of issue by “Nihon Ginkou”.

But not all revealed, probably other cause involved, for example,

  • If we get rare coins, we don’t use that.
  • The “giza zyu”(= 10yen’s coin that is made before A.D.1958), we can not used in some machines

If I have second chance, I want to revealed perfectly.

Thank you!