You can use an acoustic guitar or electric guitar, as long as they don't have nylon strings. If you want to play much slide guitar, prepare a guitar just for this job. That means using heavier strings (no "super slinky"...) and a high action (distance of the strings to the fretboard). If you have an extra guitar only for slide, you can also try out the open tunings. If you have only one and play sometimes slide or want to switch between slide and normal playing, use the standard tuning.
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The easiest and un-coolest way is to go into your guitar shop and buy one.
The coolest way, but hard to play is using a bottle.
Another way is to look around in your garage for a piece of tube, walk through a property market and look for heating copper tubes (you can make about 20 slides of 1 meter tube!) or visit a pharmacy and look for those little tablet glass bottles. You can also use the neck of a bottle (another expression for slide guitar is bottleneck guitar). There are lots of things you can use (Duane Allman, Derek Trucks and Rory Gallagher used a glass Coricidin medicine bottle, which unfortunately is no more produced, but you can get replicas!).
Some general rules:
- heavier slides sound louder (they don't vibrate itself so much)
- glass is harder than metal (usually). It slides better over the strings and gives a sharper tone
- metal slides produce a "warm" tone
- higher strings are easier to play than bass strings
Which finger should I use for slide playing? You have the choice between middle finger, ring finger and the pinky. The index finger does not work, because you need a least one finger to mute the other side of the strings. All fingers have advantages and disadvantages.
- The middle finger. The biggest finger (I said finger!) can hold a big slide and so give a fat sound for "power slide". However, you have to lift up the ring and little finger and you can't play the normal way.
- The ring finger. Duane played this way, Derek Trucks still does. The slide is big enough to get a good sound and you have two fingers left for muting the strings. But playing the normal way is hard.
- The pinky. The method of choice if you want to combine both slide and normal playing. You have three fingers for muting or playing without slide. The slides are smaller and maybe they don't cover all strings. Johnny Winter and EC play this way, Muddy Waters used it too.
Source : http://www.12bar.de/slide.php
