The despatch of prisoners to be sold into slavery
was not common until after James VI/I took the throne of England. Only
then were there foreign lands, colonies, to which transgressors could be
banished. In Europe slave labour rather than the standard serfdom, was much more
common particularly in Germany and Russia where the unfortunates were
frequently worked to death in the coal and salt mines. The situation
changed after James VI acceded to the crown of England in 1603 and in
later years transportation  to the colonies was almost routine for
even the simple offence of stealing a loaf of bread, or a piece of cloth.

Scotland, however, operated slavery 
among its own people with workers in the collieries and the salt works
being appendages that went with the industry.  The labourers who dug
coal and made the salt , chiefly in East Lothian, went to whosoever bought
the business or succeeded to the property. They could be  sold,
bartered or pawned being chattels for disposal at the will of the owner.
Where the owner had more than one mine the workers could be moved at will 
or loaned or hired out to another owner. There was no regard for the
family unit who might be rooted up because of this. The workers in the
iron stone mines and the lead mines were not so severely constrained. The
lot of the miners family was reflected in the
employment of children as young as four
in the collieries where they  acted as trap door operators, moving on
to haulers of coal, sorting the lumps from slack coal dust, and perhaps
(if they lived long enough) becoming a (relatively) better paid cutter or
`hewer` of coal.

A feature of these `slaves`, according to reports by
French soldiersin the employ of Scotland, was their insolence and
independence despite the adversities of their life. Serfdom, as in
England, never really gained a foothold in Scotland where the
relationships were more family or clan orientated. From 1606 throughout
the struggles for religious independence, slavery continued to exist. The
Glorious Revolution of 1688/9 made no change and it was not until  an
Act of Liberation in 1799 that change was effected.

To the modern mind it is detestable that even the
high minded clerics of the day took no positive action against slavery.
But it should balanced against the air of inhumanity and selfishness 
that were characteristics of the period. In 1567 for example, plague (
probably typhoid fever brought on by the unsanitary  conditions and
bad water) carried off 2,500 souls in Edinburgh. The sufferers were
banished from the city and given no medical assistance. A writer at the
time said ” Every one became so detestable to the other , and especially
the poor in the sight of the rich , as if they were beasts degenerate from
mankind”. Such was the clamour that the death penalty was ordered against 
all who visited the sick before the prescribed hour or who concealed the
presence of the plague.

The relentless barbarism and pitilessness in society
at this time  was reflected in the wholesale executions inflicted for
often petty and trivial offences.  There was no such thing as
honourable warfare and feuds both at local and national level were fought
on the lines of total extermination of the opponent. Thus to survive as a
prisoner and sold into slavery was almost an attractive alternative. By
the late 1670-1700 persecuted Covenanters accepted banishment and paid for
their passage to the colonies by entering into indentures to work for 4-5
years (as a virtual slave) and to be released with a small sum of money or
an acre or so of land to call their own. For many however, the end was in 
true slavery when agents connived with ship`s captains to sell their
passengers for a better price (about £10 for a male slave).

More about indentured servants and slaves can be found
at this site: