"18k" refers to the alloy content as 18 karat gold (18/24 gold). I have no idea about the second mark.

EDIT 1

I'm going to back off from my comment above. I now believe that the color of your ring photo is accurate. Most gold alloys are shades of yellow; There is a white alloy of gold called white gold, but I think you have a silver allow or silver plate. If it is costume jewelry, it could be something else. I read the mark as "18CI" plus a second pictorial mark. I tired a search for this mark and found myself wading through hundreds of marks with nothing similar. There is something a bit unusual about the cut of the stone. More about this in a second post.

Thanks. Thought it posted more. :)

I'm trying to figure out where/when you'd have had a "CT" instead of "KT" or "K" without a UK-style hallmark. I've never run across this style of mark with the C instead of K so I'm guessing it's not from the US.

It belonged to someone who passed away in the mid 80s, but is probably from to 1970s or earlier. The ring is pretty plain--no design on the metal whatsoever. I don't know if the style can be dated. I don't know what the stone is but it isn't glass. It's less blurry in person.

This might help,

http://www.silvercollection.it/sitemaphallmarks.html

Karats are a measure of metal purity. Carats are a measure of mass of gemstones. You may have an 18 carat Tourmaline or pink sapphire, or some other pink gemstone. Hope this helps. :)

https://sciencenotes.org/karat-vs-carat/

Thanks. Good site, Becky, even though I didn't find anything. I'll definitely keep it handy.

Interesting possibility, Viola. I was assuming it was a British influence causing it to be marked ct instead of kt or K, but you'd expect the British influence to include a bunch of hallmarks, too.

An 18 carat stone would be pretty big though, wouldn't it? I don't think this could possibly be that!

(It's not as light as it photographs--looks more like the typical red garnet in person.)

It looks like costume to me.....and I don't see 18CT on the mark....And you now know the difference between a karat and a caret,
The style looks like the past 20 years.....take it to a pawn shop....see what they will give you.....then don't sell it to them but consider what they say.

Thanks Linda. 18 Ci? It looks like an "i". I can't find info on that either.

(I do know the difference between carat and karat but also that "carat" is the UK spelling used for gold purity. But those guys mark everything so very thoroughly...I think Australia uses the CT but I am not finding much info on this stuff.)

It doesn't look like a T to me...

18c would mean gold.

Any way to get a better pic? Especially of the symbol?

There is something unusual about the cut of this stone. It does not show a flat table facet on top. Most translucent ring stones have a flat table facet on top, but this is not mandatory. A few gem cutters may cover the entire top with facets where none are at zero degrees to create something different. This type of design is normally applied to opaque stones, not clear to translucent ones.

Look carefully at the bottom side of that stone. does it have a flat facet at center? Could the stone be mounted upside down? The top side as seen may be the pavilion with the crown at bottom side. However, I can't tell the depth from this photo and the top side does seem too shallow to be a pavilion.

If you find there is a large flat (zero degree) facet on the bottom side, the stone is mounted upside down and will show much more brilliance if it is turned over. If there is a pavilion on the bottom side, it should be deeper (taller) than the top side, and it should not have a flat cutlet facet. A flat (zero degree) facet on the bottom side reduces brilliance by allowing light to leave the stone at bottom.

One caveat: A long time ago, gem cutters did place a very small flat facet at the bottom of the stone. This was thought to reduce the chance of the sharp point from being broken off. Also, if he was cutting a very hard stone such as a corundum or diamond, he might chose one of the natural crystal faces as the cutlet to reduce the amount of cutting (grinding) he needed to do. That was called the cutlet. At a later time, that flat facet was eliminated with the discovery that it let light leak out the bottom of the stone and reduced its top side brilliance (light return to the viewer).

Jem, I do see a table on the top...small, but there...

Fori have you cleaned it?

I agree that it is costume but high end costume probably from the 1950-1980s with chip diamonds in the circle of small flowers. My thoughts are that the small flowers have chip diamonds in them and the center stone may be tourmaline or other stones that were fairly inexpensive at that time. There were costume jewelry designers of the time that used real and fake, even glass, when they wanted a certain look. Mariam Haskell is one that often mixed things. Being costume it would have hallmarks other than perhaps a makers mark which it does have. Finding that maker could be interesting.

The stamp appears to be a pair of wool shears or a type of gardeners clippers with a vine over the area it would be held. Why there would be wool shears unless it denotes the last name of the maker.

C or Ct in England is the same as K over here...

Interesting! I only started looking at this because I wanted to know what it was made of and I had thought "oh. 18C white gold. Boring. But what's this other mark?"

Here it is bigger, and, alas, upside down. (Okay. Houzz turned it sideways.)

Jem, it does have a normal flat top. I know what you mean about that old cutting method--I have an art deco engagement ring and if you look straight down, it looks like there is a hole in the diamond. :)

So, this been washed but not cleaned and not polished. It doesn't seem tarnished. The "grit" you see is inside the stone, not a dirty exterior. The scuffs are scuffs. This is a better representation of the color.

Not sure I can do any better with a cell phone camera!

Since they are inside of the stone it should mean the stone is natural. I would like to suggest you take it to a jeweler who knows their stones. You may have a very expensive ring if you have what I think I am seeing. It could still be cheaply made glass. You may have to call and ask several stores to find out who in your area is knowledgeable in stones. I have a natural ruby that I was told by several that it was glass but they all wanted to purchase it at the glass price. Wanting to buy cheap means you should walk away and think about it before selling.

The pictorial mark on your ring may be an old style garden/grass shears (image below). This type of shear did not work well. If its supposed to represent an old style wool shear, it may be an Australian mark. Another possibility is it is a divider, the type used by a ship navigator, surveyor, or draftsman.

It's very pretty whatever it is...

If it's gold, I would have to have the prongs redone, tho...

I not sure what I am looking at when I view this image. I could be seeing features that are below the table, or not. My first impression was facets on top of the stone, but that could be wrong.

About those specks within the stone: Those are called inclusions and are common in natural garnets. Lab grown stones may have a few inclusions also, but these usually come from the tungsten electrodes.

My guess is your stone may be garnet if it is not glass. It does not appear to be the right shade of red for ruby, although the color of natural ruby varies. (Ruby and sapphire are chemically the same material - corundum. They vary by different colorants and impurities. Ruby is translucent to transparent and red.) Corundum is harder than garnet. Garnet and quartz have similar hardness except the hardness of garnets do vary with some samples harder than quartz.

Your stone may be dirty. A small amount of smudge on the pavilion can dull the entire stone. (Dirt on the pavilion reduces the internal reflectivity of these facets and allows light to exit the bottom of the stone. The function of the pavilion is to reflect light back toward the viewer.) To clean your stone, use rubbing alcohol with cotton balls or q-tips. clean both the top and bottom. If it was dirty, it should have more brilliance after cleaning.

Thanks all!

I was actually thinking Australia too!!--the "18 CI" mark (which on neater marks is 18CT with the T raised and underlined) seems to show up there. Shears huh? I was thinking drafting compass or an inside caliper, but sheep shears would make for a better google! (Nope. Shears aren't much better. Who would have guessed scissors are a popular jewelry motif!???)

There aren't facets on the top--it's just clear enough to show the facets beneath when slightly underlit. It's a largeish 8-sided flat spot on top. This is probably why jewelers display their stuff on black velvet and not shiny green tiles.

Darn it Jem! You made me wash away all my inclusions! It WAS dirty. And now it looks like glass. Well, not really. It's quite a bit more sparkly, even resting on a ping pong paddle.

PSA: If you have an espresso machine with the milk steamer thing, the steam makes a great jewelry cleaner. Just use tweezers to hold it.

I have a ruby that is the color of the forth picture before it was cleaned which is why I cautioned to take it to a place that knows their gems. Looking at the cleaned picture I am thinking garnet but I am also thinking those are diamonds that surround it. My reasoning for thinking they are diamonds is that the smaller stones that hold the larger stone in place in the dirty picture are yellow. A better grade was used for the larger stones. They may all be glass but it is worth getting it checked out for.

As far as those shears until she died I had a friend who grew roses and that was the only type of cutter she allowed to touch her babies. I always ended up with pinched skin and bruises when I tried to help her.

Hahahaha the espresso-making spouse would love that!

I really thought it was clean enough. :)

Well, Fori....it's best they not know. Besides, it touches nothing at all..

Maifleur, I think you're seeing the prongs as the "smaller stones"?

I'm excited to see what the jeweler says, Fori. We took my mom's faux diamond junky ring to a mall jeweler to clean and she tested it and, yes...they are diamonds :)

At any rate, even if it's all costume, it's a fun mystery!

Looks like it's about from the 50's?

Ah yes, the prongs look quite shiny in the washed photo. (There are just the two sizes--large pink and small white.) I really have no clue how to photograph jewelry and I do apologize for that.

I'd guess this style goes from midcentury to now-ish, but this particular one is from the 80s or earlier. 50s seems like a good guess to me. It's not my style, but it is definitely fun stuff.

I wish people still wore costume jewelry (instead of just fake jewelry), especially the stuff that is over-the-top silly. I have some great examples of that...but this ring is too serious. :)

Now, that you have cleaned it, its beauty shines through. Its an oval cut and apparently a good cut. If it is glass, its a nice piece of costume jewelry, but, somehow, I think its better than glass. Have a gemologist check it out.

There is no sign of a 'cat eye in your straight-on shot making me think that its RI (reflective index) is greater than for glass. Although the ring band does not show much wear, there is evidence of wear on the stone. Look at the edges of the table (the lines where the facets meet) and you will see that few of these edges have tiny chips showing that it has been knocked about from normal wear. Use a magnifier to examine the cut. However, I do not see any scratches on the stone indicating that it likely is harder than glass, possible the hardness of quartz or greater.

Do have it examined by an expert. After cleaning, it is a very nice wearable ring.

In your latest pic it definitely looks like ct not ci. The upper bar of the 2nd letter is different than the bar at the base. A capital I would have them identical.