Grab your magnifying glasses because it's time to unlock the mystery behind old-fashioned skeleton keys. Antique skeleton key identification and valuing is a bit of an art since many keys were unmarked, and tracing their provenance isn't always easy. There are clues, however, if you know where to look — and if not, we've scouted the best tips and tricks to help you out.

Are Old Antique Skeleton Keys Worth Anything?

Most individual skeleton keys sell for $10 or less, but certain styles can be worth much more. Keys with fancy bows, interesting engravings, a fascinating history, or other special features can be worth hundreds to thousands of dollars.

Harry Houdini Skeleton Keys: ~$1,000-$5,000

One of the holy grails in antique skeleton key collecting is a Harry Houdini-owned skeleton key. As an escape artist, he frequently used skeleton keys to untrap himself from the boxes and chains he locked himself in. These keys can go for a few thousand dollars at auction when they've been professionally authenticated.

For example, one small framed skeleton key with the Houdini-signed bill of sale sold for $4,250 in 2018. The bill of sale with Houdini's signature in the listing adds to its value.

Two years prior, a Houdini skeleton key with a certificate of authenticity came to auction and went for $2,400. Meanwhile, a framed skeleton key billed as Houdini's "Handcuff Key" sold for $1,195 in 2007.

These skeleton keys may not be beautifully designed, but their connection to a world-renowned figure makes them extremely valuable.

Ornate Skeleton Keys: $200-$500

More collectors are drawn to items because they're pretty than they'd like to admit. Ornate skeleton keys that have been delicately crafted always pull a little more at auction than understated ones. For example, a trio of solid-bronze finely carved Victorian skeleton keys recently sold for $245 on eBay.

Skeleton Key Ring Collections: $50-$250

The most common way skeleton keys are billed is in large lots. Imagine those movie scenes where someone pulls out a massive key ring filled with keys — that's what's being sold.

If they have the original key ring or organization system, they can go for more than when they're sold in loose lots. Recently, 117 skeleton keys on their original key ring came up for sale and sold for $250.

Do You Have a Skeleton Key?

Technically, a skeleton key is a key that features a unique shape at the end to unlock a warded lock — a lock that has some specific obstructions inside it that must be pushed out of the way with the key. However, people regularly use the term "skeleton key" to refer to several different types of keys:

• Skeleton key: Featuring a solid shaft, these keys have a pre-cut bit pattern and may fit many different locks. Because of its solid shaft, a skeleton key weighs much more than its hollow counterparts.

• Bit key: Cut from a key blank, these keys have a standard shape but a unique bit pattern to fit a specific lock.

• Barrel key: Shaped like skeleton key, these are lighter because they have a hollow shaft or barrel that allows them to slide over a post or pin in the lock. These keys are lighter in weight because their hollow shafts contain less metal.

• Interchangeable key: An Interchangeable key, or master key, often comes with changeable bits that you can adjust to fit various locks. These unique master keys are pretty uncommon.

Related: 11 Fun & Useful Ways to Repurpose Old Keys

Antique Skeleton Key Identification Guide: Top 5 Criteria

If you have an old key, there are several things to consider as you try to learn a bit more about it. Never assessed a skeleton key before? We have five criteria that can help you uncover some of your keys' hidden stories.

Skeleton Key Size

Skeleton keys come in all different sizes, from less than an inch to over five inches long. Your key's size is significant because it might give you a hint about what it was made for.

• Tiny keys: Very little keys often open jewelry boxes and other small locks.

• Small keys: Small skeleton keys, under two and a half or three inches long, sometimes open cabinets and furniture.

• Medium-sized keys: Keys ranging from two and a half to four inches long were likely made to open doors. You may find them sold with antique doorknobs.

• Very large keys: The biggest keys opened gates, large locks, and other substantial pieces.

The Key's Age

It can be very difficult to determine an old key's age, but there are a few clues that can help! A few keys are stamped with a date, but this is uncommon. Most skeleton keys you find in old drawers and boxes in your attic are from before 1940, but some keys can be very old. Look to see if the shape appears uniform or hand-molded. Handmade keys are typically older than manufactured ones.

Skeleton Key Materials

Many skeleton keys are made of brass, but some can also be made of iron. Antique brass is magnetic, while iron isn't, so if a magnet sticks to it, it's probably brass.

Skeleton Key Engravings

Some keys feature engravings that can help you establish a provenance or history. You may notice tags with hotel names or specific room numbers on them. Some keys, like Corbin keys, even have the lock manufacturer's name stamped on them. If your key has any engravings, you may have found your golden ticket to breaking open its story.

Skeleton Key Bow Shape

The bow of a key is the wider part you hold in your hand, and antique skeleton keys can feature very interesting and unique bow designs. Some feature recognizable motifs, such as lions and hearts. Interconnected knots make up the majority of these antique bow designs, and keys with interesting bows can be among the most valuable.

You Don't Want to Keep These Collectibles Under Lock & Key

Although they can be difficult to identify, old skeleton keys are cool to collect. Because they come in so many shapes and sizes, there are a plethora of options. Whether you're looking for a snazzy centerpiece for a homemade necklace or you're looking to start a low-cost collection, antique skeleton keys are the items for you.