Beautiful pieces of blue sea glass in every shade.
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Dark Blue Sea Glass: San Diego Treasure

I remember how thrilled I was to find a piece of elusive blue sea glass! The gorgeous cobalt sliver was shining up at me on a sunny day, and I squealed with delight. 

Dark blue sea glass is commonly known as cobalt sea glass, and it’s a rare find in the sea glass world. Collectors of sea glass may have to search for quite some time to find a piece. 

That’s because of every 250 or so pieces of sea glass you pick up, only one might turn out to be dark blue or cobalt sea glass. It’s definitely in the rare category. 

dark blue sea glass found in San Diego
Dark blue sea glass in my collection

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Depending on where you live, it may be easier or harder to find than that. If you’re lucky enough to be near any old glass factory locations, there’s a good chance you find blue on a regular basis.  

How rare is blue sea glass?

Blue sea glass varies in how rare it is depending on the shade.  

Blue sea glass rarity:

  • Soft blue is in the uncommon category and 1 in about every 50 pieces found might be this color. These can be windshield, window glass, fruit jars, or even old Pepsi bottles. 
  • Cobalt blue sea glass is in the rare category and 1 in approximately every 250 pieces of sea glass could be this gorgeous dark blue. It’s likely from old Noxema face cream jars, medicine bottles, and even really old poison containers. 
  • Aqua blue sea glass is in the rare category with 1 in 500 pieces of glass being this bright blue. Its origin could be Ball and Mason canning jars, soda, and glass insulators from the tops of telephone poles. 
  • Cornflower blue sea glass is a rare find since only 1 in 500 pieces of glass on the beach might be this charming shade of blue. If you are lucky to find one, it’s likely from medicine bottles such as Milk of Magnesia or decorative glass. 
  • Turquoise blue sea glass is the rarest of all blues. Only 1 in 5,000 pieces of glass on the beach will be this stunning color of blue. It’s as rare as the elusive shade of red. Its origins include specialty art glass, vases, and decorative bottles. 
several cobalt blue bottles - dark blue sea glass origin
Cobalt blue bottles form dark blue sea glass

Where does dark blue sea glass come from?

I mentioned some of the sources of cobalt and dark blue sea glass in our rarity list above, but let’s dive in a little deeper. 

In order to produce the amazing dark blue glass that forms cobalt blue sea glass, an additive is mixed in during the glass-making process. This could either be cobalt oxide or cobalt carbonate. 

Cobalt is a naturally occurring brittle metal you can find on the periodic table. With a little magic and mixing, it is made into a coloring additive for glass and other items.

How old is cobalt blue glass?

Cobalt minerals were discovered in ancient times and can be found in blue-tinted ceramics, pottery, and glass. It’s thought that cobalt colors could be found as early as 2000 BC. 

It’s even said to have been found in King Tut’s tomb! 

Produced in the mid 1800s, a coveted cobalt sea glass source is the more sinister poison bottle. It was thought that keeping poisons in brightly colored bottles would provide a better warning signal about the dangers of what was in them.  

Most pharmacists purchased glass bottles with the word poison embossed on them and many had skulls and crossbones. As you can imagine, these would be incredibly valuable pieces of cobalt sea glass to find! 

By 1907, the Fenton Art Glass Factory in West Virginia was producing amazing collections of decorative glass. 

Fenton cobalt glass products were formed into ornate pieces such as candy dishes, vases, figurines, bells, and textured jars with lids. They’re highly prized by many.

More recently, in the 1950s, cobalt glass was used for skin care creams like Noxema, and medicines such as Vicks Vapor rub and Milk of Magnesia

How much is blue sea glass worth?

For me, personally, cobalt sea glass and its other vivid blue cousins are worth a great deal. My collection is infinitely more special and beautiful with these colors as my centerpiece. 

In the open market where blue sea glass might be purchased, the value of cobalt blue sea glass might be anywhere from a few dollars to fifty dollars. The worth of blue sea glass is determined by the size, shade of color, rarity, and condition. 

I’ve seen a handful of small pieces listed on eBay for $10 as well as a beautiful naturally tumbled larger piece (perfect for jewelry) for around $35. 

Since blues of every shade are hard to come by (except the light blue soda bottles), I’m not parting with any of my blue sea glass. Each tiny and large piece in my collection represents hundreds of hours of searching and the sheer joy of finding blue.

Cobalt blue sea glass jewelry

If you’re like me, and the blues of the ocean waves thrill your heart – you might fall in love with the one-of-a-kind jewelry some sea glass artists make! 

Cobalt blue sea glass makes beautiful jewelry for beach and sea glass lovers. This jewelry is surprisingly affordable too – given that blue sea glass isn’t at all easy to find. Especially in the sizes and quality that makes good jewelry. 

My favorite pieces are on Etsy. And I’m definitely considering taking one of two pieces of my own blue sea glass and commissioning an artist to make a pendant and earrings just for me. 

You can find blue sea glass jewelry in cobalt, or any other blues you can think of. 

There are some stunning cobalt earrings that are genuine that I just love! 

And this one-of-a-kind silver locket is filled with little pieces of blue sea glass with some green added for contrast. Gorgeous!

Beautiful pieces of blue sea glass in every shade.
A variety of blue sea glass in my collection.

Fake sea glass for sale

As you’re looking for sea glass jewelry, or even rare pieces to add to your collection, beware of sea glass that’s being passed off as sea-tumbled glass when it’s not. 

Most jewelry sellers will list their man-made pieces honestly as “cultured” or “environmentally friendly” etc. This means they’ve taken discarded pieces of glass and tumbled it in a tumbler to make it appear old and weathered. 

That’s fine if you don’t mind it being man-made, but if you’re looking for the real stuff, please read listings carefully for terms such as “authentic” or “beach tumbled” etc.

sea glass identification cards with lovely pictures - collecting sea glass
My favorite sea glass identification cards.

These sea glass identification cards are my favorite go-to for all things sea glass. Including rarity, origins, color guide and so much more. I use these cards ALL the time.

How to tell if it’s sea glass

One very easy way to tell the authenticity of sea glass earrings is to look at the pair. If they match perfectly in shape, size, and color, it’s man made. 

True sea glass is impossible to find in uniform sizes and colors that are an exact match. It’s hard to find them to even sort of match. 

Also take note that authentic blue sea glass jewelry almost always has a muted or frosted coloring to it. This means it’s old and has tumbled for a while in the sea.

Sometimes real pieces of sea glass jewelry have been shined up with a little oil rubbed in to make the color more vivid, and that’s ok. 

When in doubt if the sea glass in any piece of jewelry is real, ask the seller directly if it is, and if they have an authenticity certificate for it.

various sizes and colors of dark blue sea glass
Several pieces of my dark blue sea glass.

Dark blue sea glass conclusion

I hope you’ve enjoyed the pictures and discussion about dark blue and cobalt sea glass. If you’re a collector or would like to start collecting, we have some tips for collecting sea glass in San Diego. 

And here’s a closer look at orange sea glass and how rare it actually is. 

Happy hunting!

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