- Longer Time
One of the very important tip for turning the henna darker is to leave it on your skin for a longer duration. Atleast 12 hours would be very effective.

So try to apply it before going to bed and let it stay overnight. It will helps in locking colour and getting better result
2. Clove Steam
Take a clove steam to get that gorgeous colour. Warm a few cloves in a container and run your hands over the smoke. It’s as simple as that!

Take some cloves and place them on a pan over a medium flame. Allow the cloves to heat up and then run your hands over the pan in order to soak up the fumes of the cloves. Hold our hands over the pan as long as possible.
However, make sure to maintain a safe distance and avoid exposing your skin to the heat for a long time.
3. Use A Cling Wrap
Wrapping the area with a cling wrap traps the heat to intensify the color
Once the henna is dry and flaky, wrap it up with some cling film or a thin plastic sheet. You can also use gloves and socks to wrap up your henna designs.

The wrapping of henna with cling film locks in heat and heat is possibly the best thing to help darken the colour of henna.
While you can wrap it yourself, but it is always a good idea to ask the artist to do so, for fear of spoiling the design. You can also make use of medical tape.
4. Mix some sugar with lemon juice
This is the most common remedy which helps in darkening the henna. Mix some sugar with lemon juice and use a cotton ball to apply it on your hands and feet after the henna dries up.

Apply your mehndi as it is and once it dries, apply this mixture at least thrice on your mehndi. The sugar keeps the mehndi in contact with the skin for deeper penetration, while the lemon juice acts as a catalyst for dye release and deep penetration of colour.
The myth is that lemon is the key ingredient in getting the desired colour but, the truth of the matter is that an effective sealant can be made with or without lemon juice as the real determining factor isn’t the liquid, rather the sugar.
5. Essential Oils
Adding essential oils like lemon oil, eucalyptus oil, or clove oil can darken henna. You can also mix Mahalabiya oil (an essential oil with a pine oil base) to darken henna. Essential oils contain monoterpenes, a group of alcohols often used to darken henna

6. Stay Away From Water
Use a butter knife or a card to scrape off your Mehendi instead of using water. You must avoid washing your hands and feet for at least 12 hours. Contact with water will only lighten the colour.
7. Washing Is A Prerequisite
Before you have to sit for your Mehendi make sure you wash your hands and feet with soap. This is a prerequisite as any presence of dirt or oil will hinder the absorption of henna on your skin. Washing your hands and feet ensures better absorption of henna.

8. Do Not Blow Dry Your Mehendi
You will be tempted to use something to dry your Mehendi as soon as possible, but let it dry on its own. Blow drying can lead to bleeding of your Mehendi and ruin the design and believe us, you wouldn’t want that especially when you’re getting married.
9. Shaving Or Waxing Is A Big No!
After you have applied the henna, do not shave or wax as it can scrape off the upper layer of your skin. This can also ruin your Mehendi and make it look dull.
10. Get It Done in Advance
A day or two in advance is when you should apply your mehendi. Remember that it darkens overnight, so to get the best colour on D-Day, you should apply it 2 days before your wedding ceremony.
11. Using Balms to Darken Mehndi Naturally
This step is to be followed once you get rid of all the mehndi from your hands.
After scraping off all the henna from your hands, apply balms like Vicks Vapour Rub or Tiger Blam all over your hands just like you apply hand lotion. make sure all of your henna design is covered. Leave it overnight and you’ll wake up to beautiful and dark henna design.
These balms are said to have active agents in them which help in stimulating colour development and penetration of henna into the skin. These balms create heat under your skin and darken the colour. The menthol present n the Vicks helps in darkening colour.