Crafting Spell Gems (Out of the Abyss Magic Items)

So, I am running a game with a bunch of 3rd level characters, and one of the players has read Out of the Abyss... my favourite Campaign from WotC...
Point is, he thought any Spellcaster could just cast spells into regular gemstones to create Spell Gems...

I corrected this, by pointing out the specific rules in the 2024 DMG, and for now, there's no issue...

But it got me thinking: should I treat these as Scrolls, since they are functionally pretty much the same? And regardless, how would you run your players crafting magic items? I am tempted to require new (Homebrewed) Feats, but I don't want things to be overly complicated.

So, let's chat about it, please. Inquiring minds want to know!

Is this a similar case to a Hag Eye? (Crafting a Hag Eye)

- Creating a Hag Eye. Only a hag coven can craft this item, which is made from a real eye coated in varnish and often fitted to a pendant or another wearable item.

- Spell Gem: [...] Deep gnomes created these magic gemstones and keep the creation process a secret.

In any case, I'm following the 5.5e DMG rules for crafting, so the exceptions are common Potion of Healing and Spell Scrolls:

Crafting Magic Items

The Player’s Handbook contains rules on brewing Potions of Healing and scribing Spell Scrolls. To create other magic items, follow the rules below. In these rules, “you” refers to the character crafting the magic item.

EDIT: for clarity.

I think there are a few good reasons you should probably just treat spell gem crafting as they are raw i.e permanent magical items. 

I didn't know spell gems existed as an item until recently when I was actually reading some magic items carefully. I think they're actually sick and surprisingly powerful. 

I think just by virtue of being reusable spell scrolls it makes sense that they should have the increased crafting requirements of permanent magic iteman Depending on the level of the spell, comparing on the 2024 magic item crafting table, the gem can take 3-10 times longer to craft than a scroll. It shouldn't be too difficult for players to get a return on their investment by casting their favorite spells with gems as opposed to spell scrolls. 

There are three components I would consider for crafting. Proficiencies, down time and formula/materials.

Proficiencies and downtime are probably the simplest requirements. I think you could use reduce the time to make spell gems to make it coser to the time suggested for scrolls but it's probably unnecessary if you already have regular opportunities for down time.

Jewelers tools proficiency is the most obvious for a spell gem. If your PCs need to learn and the required proficiencies I don't think having custom feats is necessary I would just let them train additional tool proficiencies if they can find a master to learn from during some downtime. Maybe use the number of tool proficiencies they already have as a baseline for what you let them learn. I feel like if players want to learn proficiencies specifically for crafting, I would let them retrain or learn one crafting proficiency for each tool proficiency their character already has. WotC also tends to require arcana proficiency, but I think every character getting arcana just to craft is a little silly. 

In the 2024 rules the last component is basically just roll to see if you can find the appropriate materials in the city or town that you're in. I like having more custom materials for items, especially with taking inspiration from the OotA lore where spell gems are a deep gnomes Trade secret. For more "average" magic items though i might just leave it at a gold cost.

What I think would be most consistent with the lore is that deep gnomes (or what ever society guards the crafting method in your setting) are not even willing to share the method to create the gems but they are willing to trade magically processed gems that the players can use to craft whatever spell gems they want. Maybe, they also have some encounters so they can collect a substance needed for the magic. Another option is you could have the PCs discover the creation method through the crafting process, maybe increasing the crafting time and or costs. Or finally if you don't want the creation process to be a challenge. Maybe there's a book in some Library that has enough details for the characters to recreate the item. Kind of like the 2024 rules.

I think having some sort of adventure to somehow learn the formula it's probably the coolest but can become tedious if your players want to craft many different magic items. 

The materials/gold cost is basically just for the DM to decide what the resource cost is for the item. Honestly I wonder what material costs are even supposed to be because the cost of the item that is being enchanted is supposed to be separate from the cost of the actual crafting itself. Do you need to buy an enchantment binding substance, a bunch of ritual magic components, maybe both. 

On a last note it always bothered me how spell scrolls didn't used to use the casters attack bonus and spell save DC. I would just change that for spell gems. 

I've found a couple substantial differences between spell gems and spell scrolls so I have a list here for anyone to reference.

The main difference which is obvious to everyone, spell gems are reusable. I feel like this has some implications that people don't think of though. You can't make a stockpile of gems the same way you would scrolls. In the case of memorized spell casters you could make enough scrolls for an entire campaign (depending on the length) before you unlearn a spell. Also say one spell gem is worth five spell scrolls, you could blow all five scrolls in the same day but you would need a day of downtime to recharge a few spell gems.

Spell gems change the casting components. Using a spell gem requires no verbal, somatic or material components as they are already accounted for during the storing of the spell. That's amazing particularly for enchantment and illusion spells because you can cast them without anyone being able to tell basically giving you free subtle spell on one predetermined spell. 

Spell gems change the action economy. You can store spells with a casting time of one action or one minute and longer. However when you use the gym to cast the spell it only takes your action. This means you can get into shenanigans like casting prayer of healing, hallow or glyph of warding as an action in or before combat.