Auspicious gems
Thai birthstones by day of the week — all eight days, and how to buy the real thing
Thailand assigns a colour to each day of the week, and the gem that carries that colour is worn for luck by people born on that day. This guide covers all eight days, including the Wednesday-night split, with buying notes for each stone.
Thailand has linked colours to the days of the week since at least the Ayutthaya period. The source is Thai astrology's nine celestial deities, one presiding over each day, each with a body colour of its own. That colour became the lucky colour of anyone born on that day — for clothes, for flowers, and eventually for gemstones.
This guide walks through the week day by day: the colour, the gems that carry it, the meaning attached to them, and what to know when buying each one. At the end there is a note on finding your day of birth, and on buying genuine stones.
A word before you read on — colour and fortune are tradition, not science. Different schools give slightly different stones. What follows is the set most widely used in the Thai jewellery trade.
Summary table
| Day of birth | Colour of the day | Principal gem | Also suitable |
|---|---|---|---|
| Sunday | Red | Ruby | Red spinel, garnet |
| Monday | Pale yellow, cream, white | Yellow sapphire | Pearl, diamond, moonstone |
| Tuesday | Pink | Pink sapphire | Pink ruby, rose quartz |
| Wednesday (day) | Green | Emerald | Jade, green sapphire, peridot |
| Wednesday (night) | Black, grey, deep purple | Black spinel | Black sapphire, smoky quartz |
| Thursday | Orange, golden yellow | Yellow sapphire | Orange sapphire, citrine |
| Friday | Blue | Blue sapphire | Aquamarine, blue topaz |
| Saturday | Purple, black | Purple sapphire | Amethyst, black spinel |
See the gems and jewellery we actually have in store, by day, on the birthstones page.
Sunday — ruby
The Sun presides over Sunday and its body colour is red. No red gem compares with ruby. In Thai tradition ruby is one of the nopparat, the nine gems of the nine planets, and it stands for the Sun directly. The meaning attached to it is power, courage and standing.
Buying notes — a fine ruby costs more per carat than a diamond of the same size. The single largest factor in price is whether it has been heated. An unheated ruby of good colour from Myanmar or Mozambique sells for several times the price of a heated one. A laboratory report that states the treatment is therefore essential. Most rubies sold in Chanthaburi have been heated; that is normal and accepted in the trade, provided the seller says so.
On a tighter budget, red spinel is an excellent alternative: a vivid red close to ruby, at a fraction of the price, and usually untreated.
In store: Sunday birthstones
Monday — yellow sapphire, pearl, diamond
The Moon has a soft yellow body colour, so Monday's colours are pale yellow, cream and white. That gives several gems to choose from. Yellow sapphire is the principal stone; pearl represents the Moon in many cultures; and white diamond belongs here too. The meaning is calm, gentleness, kindness and an understated charm.
Buying notes — most yellow sapphires on the market have been heated to even out the colour, which is widely accepted. Unheated Sri Lankan stones of a good golden yellow cost considerably more. Pearls have no grading-report system like diamonds; you have to judge lustre and surface yourself. See our guide to choosing pearls.
In store: Monday birthstones
Tuesday — pink sapphire, pink ruby
Mars in Thai tradition has a pink body colour (unlike the Western red), so Tuesday's colour is pink. The gems are pink sapphire and pink-toned ruby — the same mineral, differing only in depth of colour. The meaning is confidence, determination and a charm with force behind it.
Buying notes — there is no international standard for where "pink ruby" ends and "pink sapphire" begins. Laboratories can name the same stone differently, and the price difference is large. If a report says ruby, check which laboratory issued it. Names the trade trusts — GRS, GIA, AIGS, GIT — carry more weight.
In store: Tuesday birthstones
Wednesday (day) — emerald, jade, green sapphire
Mercury's body colour is green. Anyone born on Wednesday between 06:00 and before 18:00 has green as their colour. There are many green gems: emerald is the principal one, jade is especially popular among Thai families of Chinese descent, and green sapphire is a stone Chanthaburi is known for. The meaning is growth, negotiation and luck in trade.
Buying notes — almost every emerald in the world has been oiled to reduce visible fractures. Reports state the degree (none / minor / moderate / significant); the less, the higher the price. With jade, the question is Type A (untreated) versus B or C (bleached and resin-impregnated), and the price gap is wide. See the jade guide.
In store: Wednesday (day) birthstones
Wednesday (night) — black spinel, black sapphire
Thai astrology splits Wednesday in two. Anyone born on Wednesday from 18:00 until before 06:00 on Thursday is counted as born on Wednesday night, under Rahu. The colours are dark: black, grey and deep purple. The gems are black spinel (what the Thai trade usually means by nin) and black sapphire. The meaning is protection, steadiness and overcoming obstacles.
Many people born on a Wednesday night do not know they belong to this group, because a birth certificate records only the date. If you were born in the evening or the small hours of a Wednesday, use this group rather than Wednesday day.
Buying notes — black spinel is inexpensive, which makes it well suited to sets or to surrounding a principal stone. The thing to watch for is black glass sold as spinel. Weight and coolness to the touch are the first checks; a laboratory report settles it.
In store: Wednesday (night) birthstones
Thursday — yellow sapphire, orange sapphire
Jupiter, the teacher of the gods, has a golden-orange body colour. Thursday's colours are orange and golden yellow. The principal stones are a deeper yellow sapphire and orange sapphire, up to and including the rare and expensive padparadscha. The meaning is wisdom, learning, maturity and being held in respect.
Yellow sapphire therefore serves both Monday and Thursday. The difference is tone: pale and soft for Monday, deep and golden for Thursday.
In store: Thursday birthstones
Friday — blue sapphire
Venus has a blue body colour, so Friday's colours are light and dark blue. Blue sapphire is the definitive Friday stone, and one that Thailand is known for worldwide through the historic Kanchanaburi and Chanthaburi deposits. The meaning is love, serenity, allure and fidelity.
Buying notes — the colours the market prices highest are Royal Blue and Cornflower Blue. Most blue sapphires have been heated; unheated stones from Sri Lanka, Myanmar or Kashmir cost far more. See the blue sapphire guide on origins and heating.
In store: Friday birthstones
Saturday — purple sapphire, black spinel
Saturn has a black body colour, and Saturday's colours are purple and black. The gems are purple sapphire, amethyst and black spinel. The meaning is patience, discipline, stability and the rewards of long effort.
Saturday and Wednesday night share black spinel. What sets Saturday apart is purple; for a stone that is clearly "Saturday's", choose a purple tone.
In store: Saturday birthstones
If you are not sure which day you were born on
Birth certificates give the date, not the weekday. The easiest way to find out is to scroll the calendar on your phone back to your birth date, or search for the date with "what day of the week".
The one point of care is Wednesday: you also need to know whether the time was before or after 18:00. If it was not recorded, ask an older relative — most remember whether it was morning, afternoon or night.
How to buy the real thing
Birthstones by day are a popular gift, so imitations and synthetics circulate widely, especially for ruby, sapphire and emerald. Three rules hold.
- Ask for a laboratory report — for ruby, sapphire, emerald and diamond, a report from GIA, GIT, AIGS or GRS confirms the stone is natural, states its treatment, and in some cases its origin.
- Ask about treatment directly — heated, oiled, or untreated. A good seller answers at once and without hedging, because the price already reflects the answer.
- Buy from a shop with a physical address — Chanthaburi is the world's centre for coloured stones. Shops that have been in the town for decades have the networks to source stones directly and a reputation to protect.
Every piece at Bijouxteria lists carat weight, treatment and report number on its page. If the stone for your day is not in stock, contact us and we will source one to your budget and design the setting.
I was born at exactly midnight on a Wednesday. Is that Wednesday day or night?
Wednesday night. In Thai reckoning the night period runs from 18:00 on Wednesday until before 06:00 on Thursday, so midnight falls inside it. Anyone born after 06:00 on Thursday is simply Thursday.
Is there any harm in wearing a stone that does not match my day?
No school of thought says so. Every gem can be worn on every day. The day colour is a way of choosing a stone that reinforces, not a prohibition. Wear what you love.
What is the difference between birthstones by day and by zodiac sign?
They are separate systems. Day of birth is a Thai tradition based on the weekday; the zodiac is Western astrology based on date and month. One person has a stone under each. See our article on zodiac birthstones.
For a gift, is a ring or a pendant safer?
If you do not know the ring size, a pendant or earrings avoid the problem. If it has to be a ring, our ring-size guide explains how to find a size without the wearer knowing.